and behaviour. The mechanism of the active component of some plant-based anaphrodisiacs may be the inhibition of enzymes that catalyze the conversion of sex-hormone precursors into androstenedione, which promotes the reduction of sexual urges. Studies have demonstrated that some of these products inhibit 17β-hydroxysteroid dehydrogenase and 17,20-lyase, which catalyzes the conversion of 17α-hydroxyprogesterone to androstenedione to testosterone. In one study a group of men were given an anaphrodisiac and the effect on the metabolism of mineralocorticoids in these men was recorded. During the period of administration, the testosterone concentrations decreased and the serum 17α-hydroxyprogesterone concentrations increased. Testosterone levels fell by about 40% after administration and returned to normal after usage was discontinued. However, the actual effect of these medicines on sexual desire was not measured in the study. The amino acid 5-HTP, or 5-hydroxytryptophan, has been anecdotally reported to be a mild anaphrodisiac, as has the serotonergic empathogen MDMA, popularly known as "ecstasy". However, systematic study of these chemicals is lacking, due to the off-patent nature of 5-HTP, and the legal control of MDMA. In addition, other serotonergic euphoriant drugs, like the psychedelic LSD, have been reportedly used to drastically increase sexual pleasure. MDMA in combination with a PDE5 inhibitor (trade names Viagra, Levitra, and Cialis) is termed "sextasy". This combination increases libido and performance simultaneously. A PDE5 inhibitor taken alone has no effect on sex drive, suggesting that serotonergic euphoriants like MDMA may actually increase libido while decreasing performance, similar to alcohol. A 2003 study has found that glycyrrhizin, the compound in liquorice root, can lower levels of testosterone. The findings back up a previous study about the hormonal effects of liquorice (whose results could not be replicated in other studies in the past). The Iranian scientists came to the conclusion that the regular consumption of liquorice can lower libido in men. However, the study also showed that the level of testosterone normalizes after abstinence of liquorice within a few days and the effects completely disappear. List of putative anaphrodisiacs See also Aphrodisiac Chemical castration Categories References External links New Scientist: "The Last Word", 29 June 2002 debunks bromide in British Army tea snopes.com debunks saltpetre in U.S. Army coffee Aphrodisiacs and Anti-aphrodisiacs: Three Essays on the Powers of Reproduction by John Davenport. Anti-Valentine’s Day Food: Avoid the Sex by Feeding Them Anaphrodisiacs Drug classes defined by psychological effects Sex and drugs Psychoactive drugs Anaphrodisia