Q: The recent news about Bill Cosby and his statements that women 'need chemicals' to get in the mood for sex made me wonder: Are there any aphrodisiacs that work?  Do you need a prescription to get them? 

A: Whether there are any aphrodisiacs that work depends on the definition. The Oxford Dictionary says an aphrodisiac is "provocative of or exciting sexual desire". Scientists have generally agreed  that there is no agent you could eat, drink, inject, or apply topically that would provoke or excite sexual desire. They say it's all in your head; if a product seems to work, it's all placebo effect or misinterpretation of a physical response as a sexual response. Indeed, placebos probably are more effective here because of the predominant role the mind plays in sexual desire and performance.

Effectiveness and strength are two different issues. Spanish Fly (ground-up cantharides beetles), once touted as a strong aphrodisiac, is a prime example. It's strong all right. It irritates the urinary tract so strongly it has killed people.

In 2015, a prescription drug, Addyi (flibanserin) came on the market for pre-menopausal women, and three more drugs targeted at neurotransmitters in women's brains are in the pipeline.  About 10 percent of women are believed to have hypoactive sexual desire disorder (HSDD) also known as female sexual interest/arousal disorder (FSIAD). It all has to do with neurotransmitters. The dopamine in these women's brains that says "let's do it" is overcome by the serotonin in their brains that says "let's not."  Medicines like Addyi aim to change the relationship between dopamine and serotonin. And yes, these medicines all appear to fit the Oxford Dictionary's definition of aphrodisiacs – to provoke and  excite desire.

Addyi has not been a big seller, for several reasons. One is that in clinical trials, Addyi tablets, which are taken orally daily, increased sexual satisfaction just 0.5 times more than placebos. Also Addyi originally cost more than $800 a month and users were admonished to consume no alcohol whatsoever while taking it.

Two other female libido arousal drugs have completed their clinical trials but have yet to appear on the market. They are librido and libridos which are intended to work on both brain and body. Librido, smaller than an aspirin, contains a Viagra-like drug in a testosterone and mint coating. Instead of the Viagra-like drug, libridos contains buspirone – an antidepressant usually used to elevate mood. Separately, neither the testosterone or the other drug can lift flagging female libido, but together they are said to provide the necessary boost. Also in development is bremelanotide, which activates neurological receptors linked to sexual response. Women take it only when they want to have sex, and may drink alcohol while using it.

Testosterone is the major treatment for men with lack of desire. For male performance enhancers, (e.g., Viagra, Cialis, Levitra) to work, desire, whose origin is in the brain, is required. Antidepressants are also used to treat male lack of desire when depression is a cause.

As for non-prescription desire potions, the variety found in early writings is mind boggling and often amusing. Ancient Romans, for instance, attributed aphrodisiac qualities to items including cumin, dill, aniseed, celery seed, capers, thyme, ginger, basil, oregano, pepper, caraway, sesame, mustard, garlic, shallots, artichokes, beans, asparagus, turnips, truffles, parsnips, leeks, beets, cabbage, chicory, cucumber, radishes, lettuce, mullet, tuna, bream, octopus, mussels, sea urchin, oysters, cuttlefish, squid, crayfish, rays, eggs, honey, bird organs, insects and animal genitalia.

And how about milk of an ass mixed with bat blood?

But if you define an aphrodisiac solely as something that affects physical response, rather than desire, those do exist. Hallucinogenic plants and marijuana have been the most popular for affecting sex over the ages.

Old myths about drugs and sex die hard; new ones abound, and money is made off hopes that a drug can open the gate to a garden of sexual delights. Don't waste yours on an over-the-counter product, and please abstain from any made from any animal part – especially rhino horns. Those magnificent animals are endangered, largely because of the false belief that their horns have some aphrodisiac effect.

Patricia Bush, M.S. Ph.Dm is emeritus professor at Georgetown University School of Medicine, and Albert Wertheimer, Ph.D, MBA, is a professor at Nova Southeastern University College of Pharmacy