An aphrodisiac is a substance that increases libido when consumed. Aphrodisiacs are distinct from substances that address fertility issues such as impotence or secondary sexual (dys)function such as erectile dysfunction (ED).
The name comes from the Greek ἀφροδισιακόν, aphrodisiakon, i.e. "sexual, aphrodisiac", from aphrodisios, i.e. "pertaining to Aphrodite", the Greek goddess of love. The opposite substance is an anaphrodisiac.
Throughout human history, food, drinks, and behaviors have had a reputation for making sex more attainable and/or pleasurable. However, from a historical and scientific standpoint, the alleged results may have been mainly due to mere belief by their users that they would be effective (placebo effect). Likewise, many medicines are reported to affect libido in inconsistent or idiopathic ways: enhancing or diminishing overall sexual desire depending on the situation of subject. This further complicates the assessment process. For example, Bupropion (Wellbutrin) is known as an antidepressant that can counteract other co-prescribed antidepressants' libido-diminishing effects. However, because Wellbutrin only increases the libido in the special case that it is already impaired by related medications, it is not generally classed as an aphrodisiac.
Libido is clearly linked to levels of sex hormones, particularly testosterone. When a reduced sex drive occurs in individuals with relatively low levels of testosterone (e.g., post-menopausal women or men over age 60), testosterone supplements will often increase libido. Approaches using a number of precursors intended to raise testosterone levels have been effective in older males, but have not fared well when tested on other groups.
Some compounds that activate the melanocortin receptors MC3-R and MC4-R in the brain are effective aphrodisiacs. One compound from this class, bremelanotide, formerly known as PT-141, is undergoing clinical trials for the treatment of sexual arousal disorder and erectile dysfunction. It is intended for both men and women. Preliminary results have proven the efficacy of this drug, however development was suspended due to a side effect of increased blood pressure observed in a small number of trial subjects who administered the drug intra-nasally. On 12 August 2009, Palatin, the company developing the drug, announced positive results (none of the previous heightened blood pressure effects were observed) of a phase I clinical study where trial subjects were instead administered the drug subcutaneously. Palatin is concurrently developing a related compound they call PL-6983.