Alcohol and sex
Alcohol consumption has a number of effects on sexual behavior. The effects of alcohol are balanced between its suppressive effects on sexual physiology, which will decrease sexual activity, and its suppression of psychological inhibitions, which will increase the desire for sex.
Alcohol is a depressant. After consumption, alcohol causes the body’s systems to slow down. Often, feelings of drunkenness are associated with elation and happiness but other feelings of anger or depression can arise. Balance, judgment, and coordination are also negatively affected. One of the most significant short term side effects of alcohol is reduced inhibition. Reduced inhibitions can lead to an increase in sexual behavior.
Alcohol and sex in men
Men's sexual behaviors can be affected dramatically by alcohol. Both chronic and acute alcohol consumption have been shown in most  (but not all) studies to inhibit testosterone production in the testes. This is believed to be caused by the metabolism of alcohol reducing the NAD+/NADH ratio both in the liver and the testes; since the synthesis of testosterone requires NAD+, this tends to reduce testosterone production.
As testosterone is critical for libido and physical arousal, alcohol tends to have deleterious effects on male sexual performance. Studies have been conducted that indicate increasing levels of alcohol intoxication produce a significant degradation in male masturbatory effectiveness (MME). This degradation was measured by measuring blood alcohol concentration (BAC) and ejaculation latency. Alcohol intoxication can decrease sexual arousal, decrease pleasureability and intensity of orgasm, and increase difficulty in attaining orgasm.
Alcohol and sex in women
In many women, alcohol increases sexual arousal and desire, although it does lower the physiological signs of arousal. Women have a different response to alcohol intoxication. Studies have shown that acute alcohol consumption tends to cause increased levels of testosterone and estradiol. Since testosterone controls in part the strength of libido in women, this tends to cause an increased interest in sex. Also, because women have a higher percentage of body fat and less water in their bodies, alcohol can have a quicker, more severe impact. Women’s bodies take longer to process alcohol; more precisely, a woman's body often takes one-third longer to eliminate the substance.
Sexual behavior in women under the influence of alcohol is also different from men. Studies have shown that increased BAC is associated with longer orgasmic latencies and decreased intensity of orgasm. Some women report a greater sexual arousal with increased alcohol consumption as well as increased sensations of pleasure during orgasm. Because ejaculatory response is visual and can more easily be measured in males, orgasmic response must be measured more intimately. In studies of the female orgasm under the influence of alcohol, orgasmic latencies were measured using a vaginal photoplethysmograph, which essentially measures vaginal blood volume.
Psychologically, alcohol has also played a role in sexual behavior. It has been reported that women who were intoxicated believed they were more sexually aroused than before consumption of alcohol. This psychological effect contrasts with the physiological effects measured, but refers back to the loss of inhibitions because of alcohol. Often, alcohol can influence the capacity for a woman to feel more relaxed and in turn, be more sexual. Alcohol may be considered by some women to be a sexual “disinhibitor”.
Drug facilitated sexual assault
Drug-facilitated sexual assault (DFSA), also known as predator rape, is a sexual assault carried out after the victim has become incapacitated due to having consumed alcohol or other drugs. The unofficial term "date rape drug" came into widespread usage in the early 1990s through U.S. news media reports. Researchers say that unlike other types of rape, DFSA is not a crime of physical violence: it is a crime of sexual hedonism and entitlement. A date rape drug, also called a predator drug, is any drug that can be used to assist in the execution of drug facilitated sexual assault (DFSA). The most common types of DFSA are those in which a victim ingested drugs willingly for recreational purposes, or had them administered surreptitiously: it is the latter type of assault that the term "date rape drug" most often refers to.
Alcohol intoxication is associated with an increased risk that people will become involved in risky sexual behaviours, such as unprotected sex. It is unclear whether the two are linked or the personality types of people who often drink large amounts of alcohol are more tolerant of risk-taking.
"Beer goggles" is a slang term for the phenomenon in which consumption of alcohol lowers sexual inhibitions to the point that very little or no discretion is used when approaching or choosing sexual partners. The term is often humorously applied when an individual is observed making, or later regretting, advances towards a partner who would be deemed unattractive or inappropriate when sober. The "beer goggles" are considered to have distorted the "wearer's" vision, making unattractive people appear beautiful, or at least passably attractive.
A study published in 2003 supported the beer goggles hypothesis; however, it also found that another explanation is that regular drinkers tend to have personality traits that mean they find people more attractive, whether or not they are under the influence of alcohol at the time. A 2009 study showed that while men found adult women (who were wearing makeup) more attractive after consuming alcohol, the alcohol did not interfere with their ability to determine a woman's age.
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