Chocolate is a psychoactive food. It is made from the seeds of the tropical cacao tree, Theobroma cacao. The cacao tree was named by the 17th century Swedish naturalist, Linnaeus. The Greek term theobroma means literally "food of the gods". Chocolate has also been called the food of the devil; but the theological basis of this claim is obscure.

Cacao beans were used by the Aztecs to prepare a hot, frothy beverage with stimulant and restorative properties. Chocolate itself was reserved for warriors, nobility and priests. The Aztecs esteemed its reputed ability to confer wisdom and vitality. Taken fermented as a drink, chocolate was also used in religious ceremonies. The sacred concoction was associated with Xochiquetzal, the goddess of fertility. Emperor Montezuma allegedly drank 50 goblets a day. Aztec taxation was levied in cacao beans. 100 cacao beans could buy a slave. 12 cacao beans bought the services of courtesan.

The celebrated Italian libertine Giacomo Casanova (1725-1798) took chocolate before bedding his conquests on account of chocolate's reputation as a subtle aphrodisiac. More recently, a study of 8000 male Harvard graduates showed that chocoholics lived longer than abstainers. Their longevity may be explained by the high polyphenol levels in chocolate. Polyphenols reduce the oxidation of low-density lipoproteins and thereby protect against heart disease. Such theories are still speculative.

Placebo-controlled trials suggest chocolate consumption may subtly enhance cognitive performance. As reported by Dr Bryan Raudenbush (2006), scores for verbal and visual memory are raised by eating chocolate. Impulse-control and reaction-time are also improved. This study needs replicating.

A "symposium" at the 2007 American Association for the Advancement of Science - hyped as a potentially "mind-altering experience" - presented evidence that chocolate consumption can be good for the brain. Experiments with chocolate-fed mice suggest that flavanol-rich cocoa stimulates neurovascular activity, enhancing memory and alertness. This research was partly funded by Mars, Inc.

Coincidentally or otherwise, many of the worlds oldest supercentenarians, e.g. Jeanne Calment (1875-1997) and Sarah Knauss (1880-1999), were passionately fond of chocolate. Jeanne Calment habitually ate two pounds of chocolate per week until her physician induced her to give up sweets at the age of 119 - three years before her death aged 122. Life-extensionists are best advised to eat dark chocolate rather than the kinds of calorie-rich confectionery popular in America.

In the UK, chocolate bars laced with cannabis are popular with many victims of multiple sclerosis. This brand of psychoactive confectionery remains unlicensed.

Chocolate as we know it today dates to the inspired addition of triglyceride cocoa butter by Swiss confectioner Rodolphe Lindt in 1879. The advantage of cocoa butter is that its addition to chocolate sets a bar so that it will readily snap and then melt on the tongue. Cocoa butter begins to soften at around 75 F; it melts at around 97 F.

Today, chocolates of every description are legal, unscheduled and readily available over the counter. Some 50% of women reportedly claim to prefer chocolate to sex, though this response may depend on the attributes of the interviewer.

In 2007, a UK study suggested that eating dark chocolate was more rewarding than passionate kissing. More research is needed to replicate this result.

More than 300 different constituent compounds in chocolate have been identified. Chocolate clearly delivers far more than a brief sugar high. Yet its cocktail of psychochemical effects in the central nervous system are poorly understood. So how does it work?

CHOCOLATE : the Psychoactive Cocktail
Chocolate contains small quantities of anandamide, an endogenous cannabinoid found in the brain. Sceptics claim one would need to consume several pounds of chocolate to gain any very noticeable psychoactive effects; and eat a lot more to get fully stoned. Yet it's worth noting that N-oleolethanolamine and N-linoleoylethanolamine, two structural cousins of anandamide present in chocolate, both inhibit the metabolism of anandamide. It has been speculated that they promote and prolong the feeling of well-being induced by anandamide.

Chocolate contains caffeine. But the caffeine is present only in modest quantities. It is easily obtained from other sources. Indeed a whole ounce of milk chocolate contains no more caffeine than a typical cup of "decaffeinated" coffee.

Chocolate's theobromine content may contribute to - but seems unlikely to determine - its subtle but distinctive psychoactive profile. Surprisingly, perhaps, recent research suggests that pure theobromine may be superior to opiates as a cough medicine due to its action on the vagus nerve.

Chocolate also contains tryptophan. Tryptophan is an essential amino acid. It is the rate-limiting step in the production of the mood-modulating neurotransmitter serotonin. Enhanced serotonin function typically diminishes anxiety. Yet tryptophan can normally be obtained from other sources as well; and only an unusually low-protein, high-carbohydrate meal will significantly increase its rate of intake into the brain.

Like other palatable sweet foods, consumption of chocolate triggers the release of endorphins, the body's endogenous opiates. Enhanced endorphin-release reduces the chocolate-eater's sensitivity to pain. Endorphins probably contribute to the warm inner glow induced in susceptible chocoholics. This sensation explains why chocolate gifts are a great way to bring joy to a loved one.

Acute monthly cravings for chocolate amongst pre-menstrual women may be partly explained by its rich magnesium content. Magnesium deficiency exacerbates PMT. Before menstruation, too, levels of the hormone progesterone are high. Progesterone promotes fat storage, preventing its use as fuel; elevated pre-menstrual levels of progesterone may cause a periodic craving for fatty foods. One study reported that 91% of chocolate-cravings associated with the menstrual cycle occurred between ovulation and the start of menstruation. Chocolate cravings are admitted by 15% of men and around 40% of women. Cravings are usually most intense in the late afternoon and early evening.

Cacao and chocolate bars contain a group of neuroactive alkaloids known as tetrahydro-beta-carbolines. Tetrahydro-beta-carbolines are also found in beer, wine and liquor; they have been linked to alcoholism. But the possible role of these chemicals in chocolate addiction remains unclear.

One UK study of the human electroencephalographic (EEG) response to chocolate suggests that the odour of chocolate significantly reduces theta activity in the brain. Reduced theta activity is associated with enhanced relaxation. This study needs replication.

Perhaps chocolate's key ingredient is its phenylethylamine (PEA) "love-chemical". Yet the role of the "chocolate amphetamine" is disputed. Most if not all chocolate-derived phenylethylamine is metabolised before it reaches the CNS. Some people may be sensitive to its effects in very small quantities.

Phenylethylamine is itself a naturally occurring trace amine in the brain. Phenylethylamine releases dopamine in the mesolimbic pleasure-centres; it peaks during orgasm. Taken in unnaturally high doses, phenylethylamine can produce stereotyped behaviour more prominently even than amphetamine. Phenylethylamine has distinct binding sites but no specific neurons. It helps mediate feelings of attraction, excitement, giddiness, apprehension and euphoria; but confusingly, phenylethylamine has also been described as an endogenous anxiogen. One of its metabolites is unusually high in subjects with paranoid schizophrenia.

There is even a phenylethylamine theory of depression. Monoamine oxidase type-b has been described as phenylethylaminase; and taking a selective MAO-b inhibitor, such as selegiline (l-deprenyl, Eldepryl) or rasagiline (Azilect) can accentuate chocolate's effects. Some subjects report that bupropion (Wellbutrin, Zyban) reduces their chocolate-cravings; but other chocoholics dispute this.