The Basic Idea
By definition, aphrodisiacs are elements that evoke or stimulate sexual desire. Companies that produce drugs or concoctions that claim to enhance your sex life often mislabel these supplements as aphrodisiacs; in order to be a true aphrodisiac, they have to create desire -- not improve performance and ability. Viagra, for example, is not an aphrodisiac.
The Chemistry of Sexual Desire
Before we can determine if something works, we have to understand what it would have to do in order to work. In the case of aphrodisiacs: What happens in the body and brain when we are sexually excited? For both men and women, it all boils down to hormones -- specifically testosterone.
In other words, our sex drive is controlled by our hormone levels, with testosterone being the key. If the balance is off, things may not function as they should. When it's right, everything falls into place.
A chain reaction begins when we see, hear, feel, think, touch, smell or otherwise encounter something sexually stimulating. The process looks something like this: First, signals are sent from the limbic lobe of the brain via the nervous system to the pelvic region. These signals tell the blood vessels to dilate. This dilation creates an erection (in both men and women -- the female erectile tissues are found in the clitoris and the region around the vaginal entrance). The vessels then close so those erectile tissues stay erect. This erection is accompanied by rapid heart rate. At the same time, our brains are releasing norepinephrine and dopamine, neurotransmitters that tell our bodies that this is good and pleasurable. (For more about the chemical processes involved with love, read How Love Works.)
If we don't have enough testosterone, then interest in sex can dwindle. Other factors including stress, fatigue and depression can also have a big effect on sexual interest.