Chocolate contains about 380 different known chemicals. One of the most distinctive chemicals in chocolate is theobromine, which is similar in structure to coffee and affects the human body like a weaker form of it. Chocolate also contains phenylethylamine, which is a chemical related to amphetamine, and chemicals that resemble opioids.
Theobromine is one of the methylxanthines present in chocolate. It is a stimulant and can be used for medical purposes, including treating high blood pressure and accumulation of bodily fluids. It can also be toxic or lethal in large doses and acts as a neurotoxin causing heart, kidney and nervous system problems. It is especially harmful to dogs and animals that metabolize theobromine slowly. Typically, the darker and purer the chocolate, the greater the levels of theobromine, although the amount in individual cocoa beans can very greatly.
Some of the opioids present in chocolate are the same as those naturally found in the body and produce milder forms of the feel-good effects associated with THC and marijuana. Researchers debate whether the quantities found in chocolate are large enough to be significant. The effects of phenylethylamine in chocolate can cause changes to blood pressure and blood-sugar levels just like theobromine. Because of its association with endorphins, phenylethylamine is sometimes called the "love drug."