Hormone replacement therapy (female-to-male)
||This article needs additional citations for verification. (December 2008)|
Hormone replacement therapy (HRT) for transgender and transsexual individuals introduces hormones associated with the gender that the patient identifies with (notably testosterone for trans men and estrogen for trans women). Some intersex people also receive HRT, either starting in childhood to confirm the gender they were assigned at birth, or later in order to change the gender they were assigned at birth.
HRT causes the development of secondary sex characteristic. While HRT cannot undo the effects of a patient's first puberty, developing secondary sex characteristics associated with a different gender often allows the patient to "pass" or be seen as the gender they identify with, which causes significant social and psychological changes. Introducing synthetic hormones into the body impacts it at every level and many patient report changes in energy levels, mood, appetite, etc. The goal of HRT, and indeed all somatic treatments, is to provide patients with a more satisfying body that is more congruent with their true psychological gender identity.
Formal requirements for HRT 
The requirements for hormone replacement therapy vary immensely.
The Standards of Care for the Health of Transsexual, Transgender, and Gender Nonconforming People (SOC) require psychological counseling and for the patient to live a period of a time in the desired gender role, in order to assure that they can psychologically function in that gender role. This period is sometimes called the Real life experience (RLE). While this standard was widely followed in the 20th century, a growing number of physicians refuse to follow the Standards of Care, insisting that they are too restrictive and that inhibiting patient access to hormone therapy does more harm than good.
Some LGBT health organizations (notably Chicago's Howard Brown Health Center ) advocate for an informed consent model where the patient must only prove that they understand the risk and consent to the procedure in order to access hormone therapy.
Some individuals choose to self-administer their medication ("do-it-yourself") because they do not have access to adequate medical care (either the available doctors do not have the necessary experience or the patient cannot afford care since transition-related procedures are prohibitively expensive and rarely covered by health insurance). However, self-administration of hormones is potentially dangerous. Individuals seeking physicians who are knowledgeable and willing to treat transgender patients may wish to consult transgender support groups or a directory of LGBT-friendly doctors, in the USA for example the Gay and Lesbian Medical Association's referral service at GLMA.org.
Medical contraindications 
Relative medical contraindications are:
- Androgen-sensitive epilepsy
- Sleep apnea
- Polycythemia (elevated red blood cell count)
- Cardiac failure, renal failure, or severe hypertension susceptible to salt retention and fluid overload
- Significant liver disease
- Coronary artery disease or risk factors for this condition
- History of uterine cancer
- Bleeding disorders (for injected testosterone)
- Significant history of violent behavior
- History of breast cancer (testosterone has antiproliferative effects on most but not all breast cancers)
Types of therapy 
The half-life of testosterone in blood is about 70 minutes, so it is necessary to have a continuous supply of the hormone for masculinization.
'Depot' drug formulations are created by mixing a substance with the drug that slows its release and prolongs the action of the drug. The two primarily used forms in the US are the testosterone esters testosterone cypionate (Depo-Testosterone) and testosterone enanthate (Delatestryl) which are almost interchangeable. Enanthate is purported to be slightly better with respect to even testosterone release, but this is probably more of a concern for bodybuilders who use the drugs at higher doses (250–1000 mg/week) than the replacement doses used by transgender men (50–100 mg/week.) They are mixed with different oils, so some individuals may tolerate one better than the other. Enanthate costs more than cypionate and is more typically the one prescribed for hypogonadal males in the US. Cypionate is more popular in the US than elsewhere (especially amongst bodybuilders.) Other formulations exist but are more difficult to come by in the US. Sustanon is a formulation that mixes shorter acting and longer acting testosterone preparations that gives more even levels of testosterone with injections given every three weeks. A newly marketed formulation of injected testosterone available in Europe, Nebido (testosterone undecanoate in oil) provides significantly improved testosterone delivery with far less variation outside the eugonadal range than other formulations with injections required only four times yearly. However, each quarterly dose requires injection of 4ml which may require multiple simultaneous injections. Nebido is also much more expensive and currently unavailable in the United States.
The adverse side effects of injected testosterone esters are generally associated with high peak levels in the first few days after an injection. Some side effects may be ameliorated by using a shorter dosing interval (weekly or every ten days instead of twice monthly with enanthate or cypionate.) 100 mg weekly gives a much lower peak level of testosterone than does 200 mg every two weeks, while still maintaining the same total dose of androgen. This benefit must be weighed against the discomfort and inconvenience of doubling the number of injections.
Injected testosterone esters should be started at a low dose and titrated upwards based on trough levels (blood levels drawn just before your next shot.) A trough level of 500 ng/dl is sought. (Normal range for a biological male is 290 to 900 ng/dl.)
Both testosterone patches, creams and gels are available. Both approximate normal physiological levels of testosterone better than the higher peaks associated with injection. Both can cause local skin irritation (more so with the patches.)
Patches slowly diffuse testosterone through the skin and are replaced daily. The cost varies, as with all medication, from country to country, it is about $150/month in the US, and about 60 Euros in Germany.
Transdermal testosterone is available throughout the world under the brand names Andromen Forte, Androgel, Testogel and Testim. They are absorbed quickly when applied and produce a temporary drug depot in the skin which diffuses into the circulation, peaking at 4 hours and decreasing slowly over the rest of the day. The cost varies, as with all medication, from country to country, from as little as $50/month to about $280/month (in US Dollars).
Transdermal testosterone poses a risk of inadvertent exposure to others who come in contact with the patient's skin. This is most important for patients whose intimate partners are pregnant or those who are parents of young children as both of these groups are more vulnerable to the masculinizing effects of androgens. Case reports of significant virilization of young children after exposure to topical androgen preparations (both prescription and 'supplement' products) used by their caregivers demonstrates this very real risk.
Subcutaneous pellets 
6-12 pellets are inserted under the skin every three months. This must be done in a physician's office, but is a relatively minor procedure done under local anesthetic. Pellets cost about $60 each, so the cost is greater than injected testosterone when the cost of the physician visit and procedure are included. The primary advantages of Testopel are that it gives a much more constant blood level of testosterone yet requires attention only four times yearly.
Not frequently used in the US, sometimes used in Europe. Once absorbed from the GI tract testosterone is shunted (at very high blood levels) to the liver where it can cause liver damage and worsens some of the adverse effects of testosterone - lower SHBG levels, lower HDL (good) cholesterol. In addition, the ‘first pass’ metabolism of the liver also may result in testosterone levels too low to provide satisfactory masculinization and suppress menses. The safest of the oral formulations is Andriol (testosterone undecanoate) which is not available in the US.
In 2003 the FDA approved a buccal form of testosterone (Striant.) Sublingual testosterone can also be made by some compounding pharmacies. Cost for Striant is greater than other formulations ($180–210/month.) Testosterone is absorbed through the oral mucosa and avoids the 'first pass metabolism' in the liver which is cause of many of the adverse effect with oral testosterone. The lozenges can cause gum irritation, taste changes, and headache but most side effects diminish after two weeks. The lozenge is 'mucoadhesive' and must be applied twice daily.
GnRH agonists 
In both sexes, the hypothalamus releases GnRH (gonadotropin-releasing hormone) to stimulate the pituitary to produce LH (luteinizing hormone) and FSH (follicle-stimulating hormone) which in turn cause the gonads to produce sex steroids. In adolescents of either sex with relevant indicators, GnRH agonists, such as nafarelin can be used to suspend the advance of sex steroid induced, inappropriate pubertal changes for a period without inducing any changes in the gender-appropriate direction. GnRH agonists work by initially over stimulating the pituitary then rapidly desensitizing it to the effects of GnRH. Over a period of weeks, gonadal androgen production is greatly reduced. There is considerable controversy over the earliest age, and for how long it is clinically, morally and legally safe to do this. The Harry Benjamin International Gender Dysphoria Association Standards of Care permit from Tanner Stage 2, but do not allow the addition of gender-appropriate hormones until 16, which could be five or more years. The sex steroids do have important other functions. The high cost of GnRH agonists is often a significant factor.
Progestin injections 
Depo-Provera (depot medroxyprogesterone acetate, or DMPA) may be injected every three months just as it is used for contraception. Generally after the first cycle, menses are greatly reduced or eliminated. This may be useful for transgender men prior to initiation of testosterone therapy.
Andro ‘Pro-hormones’: Androstenedione, 4-androstenediol, 5-androstenediol, 19-androstenediol, and 19-norandrostenediol are sold as supplements that are purported to increase serum testosterone, increase muscle mass, decrease fat, elevate mood, and increase sexual performance (i.e. many of the effects transgender men seek with androgen therapy.) However, there is no good medical evidence that the pro-hormones do any of these things. However, there is evidence that ingestion of these substances can cause elevated estrogen levels, and decreases in HDL (good) cholesterol.
Effects of HRT 
- Increased musculature and decreased body fat.
- The development of facial and body hair.
- Deepening of the voice.
Irreversible changes 
- Deepening of the voice.
- Growth of facial and body hair.
- Male pattern baldness (in some individuals).
- Enlargement of the clitoris.
- Growth spurt and closure of growth plates if given before the end of puberty.
- Possible shrinking and/or softening of breasts, although this is due to changes in fat tissue.
Reversible changes 
- Increased libido.
- Redistribution of body fat.
- Cessation of ovulation and menstruation.
- Further muscle development (especially upper body).
- Increased sweat and changes in body odor.
- Prominence of veins and coarser skin.
- Acne (especially in the first few years of therapy).
- Alterations in blood lipids (cholesterol and triglycerides).
- Increased red blood cell count.
The psychological changes are harder to define, since HRT is usually the first physical action that takes place when transitioning. This fact alone has a significant psychological impact, which is hard to distinguish from hormonally induced changes. Most trans men report an increase of energy and an increased sex drive. Many also report feeling more confident.
While a high level of testosterone is often associated with an increase in aggression, this is not a noticeable effect in most trans men. HRT doses of testosterone are much lower than the typical doses taken by steroid-using athletes, and create testosterone levels comparable to those of most natal men. These levels of testosterone have not been proven to cause more aggression than comparable levels of estrogen. It is assumed that the effect of the start of physical treatment is such a relief, and decreases pre-existing aggression so much, that the overall level of aggression actually decreases.
What HRT cannot change 
A number of skeletal and cartilaginous changes take place after the onset of puberty at various rates and times. Sometime in the late teen years epiphyseal closure (in other words, the ends of bones are fused closed) takes place and the length of bones is fixed for life. Consequently total height and the length of arms, legs, hands, and feet are not affected by HRT. However, details of bone shape change throughout life, bones becoming heavier and more deeply sculptured under the influence of testosterone. Many of these differences are described in the Desmond Morris book Manwatching.
- Pelvis: The pelvis in females tends to be wider than in males and tilted forward; the pelvis in males tends to be more circular and tilted upwards.
- Hands: Male hands and feet tend to be larger than female hands and feet in persons of equal height.
- Upper Arm: The upper arm in females tends to be significantly longer (about 1") than in males of the same height.
- Head: Females tend to have smaller heads than males of the same height.
- Chest: Female rib cages tend to be narrower than those of males in the same height.
- In biological men, testosterone levels that are either significantly above or below normal are associated with increase cardiovascular risk. This may be causative or simply a correlation.
- A single retrospective study in the medical literature of 293 trans men treated with testosterone (range of 2 months to 41 years) by the Amsterdam Gender Dysphoria Clinic from 1975 to 1994 showed no increase in cardiovascular mortality or morbidity when compared with the general female Dutch population. (As with all scientific studies, this does not conclusively prove that no causal link exists. A small to moderate detrimental effect remains a possibility, though a very large effect is more unlikely.)
- Androgen therapy can adversely affect the blood lipid profile by causing decreases in HDL (good) cholesterol, increases in LDL (bad) cholesterol, and increases in triglycerides.
- Androgen therapy redistributes the fat toward abdominal obesity, which is associated with increased cardiovascular risk rather than fat carried on the buttocks and hips.
- Androgen therapy can cause weight gain and decreased insulin sensitivity (perhaps worsening a predisposition to develop Type II diabetes.)
- Androgen therapy effects are not all negative, however. Acutely it causes dilation of the coronary arteries, and in men with testosterone levels within the normal physiological range, higher levels are actually associated with a slight decrease in cardiovascular disease.
- Supra-physiological levels of androgens (generally due to abuse) are associated with significantly increased risks of strokes and heart attacks (even in the young.)
- Cardiovascular risk factors are more than additive. (If high blood pressure is worth 10 and smoking is worth 10, together they are worth more than 20.) So for transgendered men, the addition of risk with androgen therapy makes improving modifiable risk factors more important.
- The most important modifiable risk factor for many men is smoking.
- The action of testosterone on hair follicles is mainly due to the more potent androgen, dihydrotestosterone, DHT.
- With androgen therapy, genetics primarily determines how much hair will develop (and where) as well as whether male pattern baldness will develop.
- Testosterone is converted (within the cells of the hair follicle's dermal papilla) by 5-alpha reductase to DHT. There are two forms of this enzyme: type 1 and 2. However, type 2 is the form that is important to the development of male pattern baldness. Male pseudohermaphrodites with congenital deficiency of type 2 5-alpha reductase (but functional Type 1) never develop male pattern baldness.
Gynecological effects 
- Menses should cease within 5 months of testosterone therapy (often sooner.) If bleeding continues past 5 months, trans men must see a gynecologist.
- Clitoromegaly occurs, and frequently reaches its apex within 2–3 years of therapy. Sizes generally range from 3–8 cm with 4–5 cm being about average. This is genetically determined, but some physicians advocate topical clitoral testosterone as an adjunct to growth before metaidioplasty. However, this testosterone is absorbed and should be calculated into your total regimen.
- After long-term androgen therapy, ovaries may develop polycystic ovary syndrome (PCOS) morphology. (In both PCOS and transgender men there is an up-regulation of testosterone receptors in the ovaries.)
- Untreated PCOS is associated with a possibly increased risk of endometrial cancer as well as decreased fertility.
- It is unknown whether the risk of ovarian cancer is increased, decreased or unchanged in transgender men compared to women. It is unlikely to be determined in the near future because ovarian cancer is a relatively rare disease and the population of transgender men is too small to do the appropriate study. However, it has been recommended by some physicians that transgender men have an oophorectomy within 2–5 years of starting androgen therapy due to the possible increased risk. (Note: Testosterone dose can frequently be decreased after oophorectomy.)
- The risk of endometrial cancer is similarly unknown. However, A high prevalence of endometrial hyperplasia has been noted in a small study of transgender men undergoing hysterectomy. (Futterweit W, and Deligdisch L. “Histopathological effects of exogenously administered testosterone in 19 female to male transsexuals.” J Clin Endo & Metab. 62(1):16-21. 1986.)
Frequently the first sign of endometrial cancer is bleeding in post-menopausal women. Transgender men who have any bleeding after the cessation of menses with androgen therapy should have an endometrial biopsy (and possibly an ultrasound) done to rule-out endometrial cancer.
- Some sources recommend endometrial ultrasounds every two years. Testosterone usually causes atrophy of the endometrium. Any transgender man with an endometrium that is not thinned on ultrasound should have a biopsy to evaluate for endometrial cancer and possibly use progesterone to cause sloughing of the endometrium. Vaginal bleeding from progesterone may be emotionally uncomfortable for a trans man, but is medically preferable to developing endometrial cancer.
- Until recently, any adult with a uterus/cervix was advised to have a Pap smear yearly. This interval might be increased to every 2–3 years for certain people on the advice of a gynecologist. However, recent research has linked cervical cancer to a sexually transmitted virus; trans men who have never had vaginal sex may not be at risk. However, since the long-term effects of testosterone on cervical tissues are not well understood, Pap smears may be considered a general precaution.
- Some transgender men report a decrease in breast size with androgen therapy. However, no morphological changes were found when this was studied and likely it is due to loss of fat in the breasts.
- Androgen therapy (and suppression of estrogen production) may cause vaginal atrophy and dryness, which may result in dyspareunia (painful vaginal intercourse.) This can be alleviated with topical estrogen cream.
- Most transgender men report a significantly increased libido. Some report that this decreases somewhat after several years on testosterone. (Natural testosterone levels peak in women just before ovulation which may account for the mid-cycle increase in libido many women experience.)
- As the age at which transgender people begin therapy decreases, retention of reproductive potential becomes more important.
- If a transgender man has not undergone hysterectomy and oophorectomy, he may regain fertility on cessation of testosterone. With the ovarian changes of long-term androgen therapy, however, it may require months of cessation of testosterone and possibly assistive reproductive technology to become pregnant. Testosterone must be withheld for the duration of pregnancy.
- If a transgender man is planning on having a hysterectomy/oophorectomy, future reproduction may still be preserved by:
- Oocyte banking – hormonal stimulation to ‘hyper-ovulate’ with transvaginal oocyte harvest for freezing. Previously using the "slow-freezing" cryopreservation method there were very poor survival rates of banked oocytes. However, the advent of vitrification, a rapid freezing process, has made oocyte cryopreservation a viable option for fertility preservation. Allows the possibility for eggs to later be fertilized and be placed in a surrogate, as opposed to a transgender man having to carry the pregnancy himself.
- Embryo banking – oocyte harvest as above with immediate fertilization and banking of the embryo. The sperm donor must be chosen before oophorectomy. Allows the possibility for embryos to later be placed in a surrogate, as opposed to a transgender man having to carry the pregnancy himself.
- Ovarian tissue banking – Ovarian tissue is frozen after oophorectomy. Even after long term androgen therapy, ovaries usually retain usable follicles. Eventual use of frozen ovaries will require replantation into the transgender man for stimulation and harvest, but may eventually be possible in a lab as techniques for tissue culture improve. This option does not usually allow for placement into a surrogate as it may require the use of immunosuppressants on the part of the surrogate.
- Both estrogens and androgens are necessary in both biological males and females for healthy bone. (Young healthy women produce about 10 mg of testosterone monthly. Higher bone mineral density in males is associated with higher serum estrogen.)
- Bone is not static. It is constantly being reabsorbed and created. Osteoporosis results when bone formation occurs at a rate less than bone resorption.
- Estrogen is the predominant sex hormone that slows bone loss (even in men.)
- Both estrogen and testosterone help stimulate bone formation (T, especially at puberty.)
- Testosterone may cause an increase in cortical bone thickness in transgender men (however this does not necessarily translate to a greater mechanical stability.)
- Transgender men who have been oophorectomized must continue androgen therapy to avoid premature osteoporosis. Estrogen supplementation is theoretically not usually necessary, as some of the injected testosterone will be aromatized into estrogen sufficient to maintain bone (as it does in biological men.) However, a single small study of trans men after oophorectomy demonstrated that androgens alone may be insufficient to retard bone loss. (van Kesteren P, et al. “Long-term follow-up of bone mineral density and bone metabolism in transsexuals treated with cross-sex hormones.” Clin Endocrin. 48(3):347-54. 1998.) It is likely the case that pre-oophorectomy, residual estrogen production is protective. However, after oophorectomy, some trans men may have insufficient estrogen to retard bone loss.
- Some physicians advocate a Dexa (bone density) scan at the time of oophorectomy and every year or two thereafter to diagnose osteoporosis before it becomes severe enough to be symptomatic. This is important because treatment of osteoporosis is most effective if done early.
- Daily calcium supplementation and possibly Vitamin D is probably a good idea for most transgender men, but it is even more important after removal of the ovaries.
Facial changes develop gradually over time, and sexual dimorphism (physical difference between the sexes) tends to increase with age. Within a population of similar body size and ethnicity:
- Brow: Males tend to develop heavier bony brows than females.
- Cheeks: Female cheeks tend to be fuller and more rounded. Under the influence of estrogen, fat is deposited beneath the skin and overall facial and body contours become softer. This is reversed by androgens.
- Nose: The tips of the nasal bones tend to grow more in males than females, creating a larger (longer or wider) nose.
- Jaw: The jaw in males tends to grow wider and more deeply sculptured than in females.
- Larynx: At puberty, the bones and cartilage of the voicebox tend to enlarge less in females than males. In some males, the larynx becomes visible as a bony "Adam's apple."
- Lips: Females tend to have thicker, fleshier lips than males of the same size due to estrogen.
Drug interactions 
Testosterone (and all the sex steroids) are metabolized by the Cytochrome P-450 enzyme system in the liver. (Specifically CYP3A.) There are certain drugs that increase or decrease the activity of this enzyme and may cause increased or decreased levels of testosterone and other sex steroids.
- Cyt P-450 Inducers – May cause decreased levels of testosterone (and other sex steroid) levels: Phenobarbital and Dilantin (seizure medicines,) Rifampin (antibiotic,) and Alcohol.
- Cyt P-450 Inhibitors – May cause increased levels of testosterone: Serzone, Prozac, Paxil (antidepressants,) Sporanox, Diflucan, and other ‘azole’ antifungals, Tagamet (anti-ulcer agent that can cause gynecomastia in men because of this effect.) Biaxin and other ‘erythromycin type’ antibiotics, Protease Inhibitors (HIV treatment.)
Testosterone can also alter the effects of other drugs:
- Increases the blood thinning effect of Coumadin (warfarin).
- Decreases the effectiveness of Inderal (propranolol) a blood-pressure medicine.
- Increases the effect of some oral medicines for diabetes and can cause dangerously low blood sugar levels.
Because of these interactions, it is imperative that trans men tell any health care provider that he sees for any reason that he is on androgen therapy (and any other medication or supplement that he takes.)
Obstructive sleep apnea 
- OSA may be worsened or unmasked by androgen therapy.
- Risk is greater in transgender men who are obese, smoke, or have COPD (Chronic Obstructive Pulmonary Disease.)
- Untreated OSA may have significant adverse effects on the heart, blood pressure, mood, and may cause headaches and worsen seizure disorders.
- Symptoms of OSA are noisy sleeping (snoring,) excessive daytime sleepiness, morning headache, personality changes, and problems with judgment, memory, and attention.
- Increased red blood cell mass usually from overproduction by the bone marrow.
- Testosterone (frequently in large doses) was previously used to treat anemia from bone marrow failure.
- A transgender man's hematocrit (the percentage of whole blood made up of red blood cells) should be judged against normal age adjusted values for men.
- Therapy is via phlebotomy (periodic therapeutic blood draws similar to blood donation.)
- Tendency to become polycythemic worsens with age.
- Worse with injected testosterone (especially with longer intervals between doses) than with oral, transdermal, or Testopel. (Increase in RBCs occurs with the very high peaks from injection. So decreasing dose and interval to 7–10 days instead of 14 may help.)
- Severe polycythemia predisposes to both venous and arterial thrombosis (blood clots) such as: deep venous thrombosis, pulmonary embolism, heart attack, and stroke.
- Aspirin may decrease the risk
- Increased activity of oil and sweat glands.
- Change in body odor – less sweet and musky, more metallic and acrid.
- If severe odor is a problem, an antibacterial soap like chlorhexidine may be used in the armpits when showering. After 1–2 weeks of daily use, a noticeable decrease in odor should occur.
- Acne: generally worse the first few years of testosterone therapy (mimicking a second puberty.) Can be treated with standard acne therapy. Initial treatment is with increased cleansing (at least twice daily) with an anti-acne or oil reducing scrub. If this doesn't work, additional therapy may be prescribed by a physician.
- Some physicians see acne as a contraindication to increasing testosterone dose.
- There is a risk of liver damage and liver cancer with all testosterone formulations, but this is minimal with all forms except oral or unless very high levels are administered. However, as with any drug that carries even a small risk of liver damage, liver function tests (or at least ALT) should be periodically monitored.
- Headaches: Pre-existing migraine headaches can be significantly worsened with androgen therapy. Headaches can also become problematic in men without prior headache disorders.
- Epilepsy: some seizure disorders are androgen-dependent. These may be worsened or (very rarely) unmasked with androgen therapy.
- Sleep deprivation worsens almost all seizure disorders, so concurrent obstructive sleep apnea caused or worsened by androgen therapy may also be responsible.
- Some transgender men report mood swings, increased anger, and increased aggressiveness after starting androgen therapy.
- Many transgender men, however, report improved mood, decreased emotional lability, and a lessening of anger and aggression.
- Recent studies have found that cross-hormone therapy in trans men results in an increase in brain volume up to male proportions.
- Testosterone increases body weight (and increases appetite.) The form that this weight gain will take depends on diet and exercise as well as genetic factors. Since testosterone has anabolic effects, gain of lean muscle mass will be easier than it previously was for transgender men. Moderate amounts of exercise will cause greater gains and will ameliorate some of the adverse effects of testosterone.
- Many transgender men report an increased energy level, decreased need for sleep, and increased alertness after testosterone therapy.
- In biological men, abnormally high or low levels of testosterone are both associated with insulin resistance (which eventually can result in Type II diabetes.) So mid-normal levels of testosterone are the target for androgen therapy.
- In women, increased levels of either estrogen or androgens are associated with decreased insulin sensitivity (which may predispose to diabetes.) In a study of transgender males and females, decreased insulin sensitivity was found in both populations after four months or hormonal treatment. (Polderman K, et al. “Induction of insulin resistance by androgens and estrogens.” J Clin Endo Metab. 79(1):265-71. 1994.)
Hormone levels 
Israel et al. have suggested that for pre-castration FTM individuals, therapeutic testosterone levels should optimally fall within the normal male range, whereas estrogen levels should optimally fall within the normal female range. Before castration, it is difficult and usually impractical to fully suppress estrogen levels into the normal male range, especially with exogenous testosterone aromatizing into estrogen, hence why the female ranges are referenced instead. In post-castration FTM individuals, Israel et al. recommend that both testosterone and estrogen levels fall exactly within the normal male ranges. See the table below for all of the precise values they suggest.
|Hormone||Bio. female ref. range||Bio. male ref. range||Optimal trans. female (MTF) range||Optimal trans. male (FTM) range|
|Estrogen (total)||40–450 pg/mL||< 40 pg/mL||400–800 pg/mL (pre-castration)
40–400 pg/mL (post-castration)
|< 400 pg/mL (pre-castration)
< 40 pg/mL (post-castration)
|Testosterone (total)||25–95 ng/dL||225–900 ng/dL||95–225 ng/dL (pre-castration)
25–95 ng/dL (post-castration)
|225–900 ng/dL (pre-castration)
225–900 ng/dL (post-castration)
The optimal ranges listed for testosterone only apply to individuals taking bioidentical hormones (i.e., testosterone, including esters) and do not apply to those taking synthetic or other preparations such as androgenic anabolic steroids (e.g., nandrolone).
Male and female reference ranges for hormones and other compounds are not exact and usually vary slightly depending on the source referenced. The same applies to optimal FTM (and MTF) ranges, naturally.
See also 
- "The Harry Benjamin International Gender Dysphoria Association's Standards Of Care For Gender Identity Disorders, Sixth Version". February, 2001. Retrieved 2011-12-14.
- Schreiber, Leslie. "Howard Brown Health Center Establishes Transgender Hormone Protocol". www.howardbrown.org. Howard Brown. Retrieved 2011-08-25.
- "THInCing About Hormones?: Hormone FAQs". Retrieved 2011-12-14.
- Hulshoff, Cohen-Kettenis et al. (July 2006). "Changing your sex changes your brain: influences of testosterone and estrogen on adult human brain structure". European Journal of Endocrinology 155 (155): 107–114. doi:10.1530/eje.1.02248. ISSN 0804-4643.
- Gianna E. Israel; Donald E. Tarver; Joy Diane Shaffer (26 April 2001). Transgender Care: Recommended Guidelines, Practical Information, and Personal Accounts. Temple University Press. p. 69. ISBN 978-1-56639-852-7. Retrieved 18 July 2012.
- Female-to-Male.org Testosterone HRT Guide Detailed information about testosterone HRT
- FTM Hormone Information - Very informative with different topics than this article
- Tom Waddell Clinic Transgender Protocol - MTF and FTM clinical protocols aimed at providers
- Medical Therapy and Health Maintenance for Transgender Men: A Guide For Health Care Providers: a free online medical book.
- Testosterone cypionate vs. enanthate