PT-141 (aka bremelanotide) is an experimental pharmaceutical that is undergoing testing for FDA approval to treat low libido (an aphrodisiac). PT-141 was discovered in an attempt to develop a molecule that would turn on the suntan response without exposing the skin to ultraviolet light. Although PT-141 did not trigger tanning, it did have a curious side effect on the libido.

The most recent study on bremelanotide was published in July, 2006, and it found that it increased sexual desire in pre-menopausal women with sexual arousal disorder. Among the women who engaged in intercourse within 24 hours after taking PT-141 or a placebo, those who received the drug reported greater satisfaction than those who took a placebo. In another standard measure of arousal, Bremelanotide did not increase blood flow to the vagina, indicating that the effect was more mental than physical. Research citation

If this chemical does pass all the tests needed to get FDA approval, it will still be several years before your doctor can prescribe it. A grey/black market for bremelanotide has already started - a Chinese chemical company (biopna.com) includes it among the peptides and specialty chemicals it sells. Here is how they position their product:

We can tell you how to make the spray formulation to be used directly. We can provide you this material which is in stock,the purity will be 95%,98%,or on your request,like 40%, 50%, and so on. The bioactivity showed that this material we made really work well.

Some have argued that bremelanotide is the first true aphrodisiac, as it appears to act directly on the brain centers responsible for arousal. By their arguments, drugs like Viagra are not aphrodisiacs, as they act only on the genital tissue responsible for an erection. The aphrodisiology.com definition is that anything that enhances love and/or sex can be considered an aphrodisiac. The fact that bremelanotide does not increase vaginal blood flow indicates that it is not the perfect aphrodisiac - it increases desire, but if that desire remains in the brain and is not transmitted to the loins ... ?