|Systematic (IUPAC) name|
|Legal status||P(UK) for topical use, otherwise POM. Cannot be prescribed on the NHS.|
|Routes||Oral / topical|
|ATC code||C02 D11|
|Mol. mass||209.251 g/mol|
| (what is this?)
Minoxidil is an antihypertensive vasodilator medication. It also slows or stops hair loss and promotes hair regrowth. Now off-patent, it is available over-the-counter for the treatment of androgenic alopecia. Minoxidil must be used indefinitely for continued support of existing hair follicles and the maintenance of any experienced hair regrowth. It is marketed under many trade names, including Avacor Physician's Formulation, Loniten (oral), Mintop, Amexidil, Rogaine, Spectral.DNC, and Vanarex. Kopexil is a derivative of minoxidil missing the piperidine substituent.
Originally, minoxidil was used exclusively as an oral drug (with the trade name 'Loniten') to treat high blood pressure. However, it was discovered to have an interesting side effect: hair growth. Minoxidil may cause increased growth or darkening of fine body hairs, or in some cases, significant hair growth. When the medication is discontinued, the hair loss will return to normal rate within 30 to 60 days. Upjohn Corporation produced a topical solution that contained 2% minoxidil to be used to treat baldness and hair loss, under the brand name Rogaine in the United States and Canada, and Regaine in Europe and the Asia-Pacific. The patent on minoxidil expired February 11, 1996. Treatments usually include a 5% concentration solution that is designed for men, and a 2% concentration solution for women.  While the drug is available in the United Kingdom, it cannot be prescribed on the NHS, so patients must either buy it over-the-counter or have a private prescription for it.
The mechanism by which minoxidil promotes hair growth is not fully understood. Minoxidil contains the nitric oxide chemical moiety and may act as a nitric oxide agonist. Similarly, minoxidil is a potassium channel opener, causing hyperpolarization of cell membranes. Minoxidil is less effective when there is a large area of hair loss. In addition, its effectiveness has largely been demonstrated in younger men who have experienced hair loss for less than 5 years. Minoxidil use is indicated for central (vertex) hair loss only. Minoxidil is also a vasodilator. Hypothetically, by widening blood vessels and opening potassium channels, it allows more oxygen, blood, and nutrients to the follicle. This may cause follicles in the telogen phase to shed, which are then replaced by thicker hairs in a new anagen phase.
Side effects 
Common side effects of minoxidil include burning or irritation of the eye, itching, redness or irritation at the treated area, as well as unwanted hair growth elsewhere on the body. Users should stop treatment and seek medical attention right away if they experience any of the following serious side effects: severe allergic reactions (e.g. rash, hives, itching, difficulty breathing, tightness in the chest, or swelling of the mouth, face, lips, or tongue), chest pain, dizziness, fainting, tachycardia (rapid heartbeat), sudden and unexplained weight gain, or swelling of the hands and feet.
Alcohol and propylene glycol present in some topical preparations may dry the scalp, resulting in dandruff and contact dermatitis. Some formulations of minoxidil substitute lipid Nanosomes in order to reduce contact dermatitis from the alcohol and propylene glycol vehicle.
Paradoxically, hair loss is a common side effect of minoxidil treatment. Manufacturers note that minoxidil-induced hair loss is a common side effect and describe the process as "shedding". Although this phenomenon demonstrates that minoxidil is indeed affecting hair follicles, manufacturers offer no guarantee that the new hair loss will be replaced with hair growth. The speculated reason for this shedding is the encouragement of hairs already in the telogen phase to shed early.
Side effects of oral minoxidil may include swelling of the face and extremities, rapid and irregular heartbeat, lightheadedness, cardiac lesions, and focal necrosis of the papillary muscle and subendocardial areas of the left ventricle. There have been cases of allergic reactions to minoxidil or the non-active ingredient propylene glycol, which is found in some topical minoxidil formulations. Pseudoacromegaly is an extremely rare side effect reported with large doses of oral minoxidil.
Although not documented on the label, some patients report side effects of dry skin, dark under-eye circles, and skin redness. Studies have shown that minoxidil can cause collagen depletion in vitro as it is a lysyl hydroxylase inhibitor, an enzyme which is key in collagen production.
Minoxidil needs to be applied once or the recommended twice daily, and may be used indefinitely for continued support of existing hair follicles and the maintenance of any experienced hair regrowth. To achieve maximum effect, the solution should be in contact with the scalp for at least 4 hours before allowing hair to get wet. Minoxidil stimulates hair follicles and growth, but does not reduce DHT or the enzyme responsible for its accumulation around the hair follicle, 5-alpha reductase, which is the primary mediator of male pattern baldness in genetically susceptible individuals. Therefore, when treatment is stopped, the DHT has its expected effect of shrinking and ultimately destroying the genetically predisposed hair follicles.
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