 Amphetamine and methamphetamine are phenethylamine derivatives which are known to increase libido and cause frequent or prolonged erections as potential side effects, particularly at high supratherapeutic doses where sexual hyperexcitability and hypersexuality can occur; however, in some individuals who use these drugs, libido is reduced.Libido in males is linked to levels of sex hormones, particularly testosterone.When a reduced sex drive occurs in individuals with relatively low levels of testosterone, particularly in postmenopausal women or men over age 60, dietary supplements that are purported to increase serum testosterone concentrations have been used with intent to increase libido, although with limited benefit.