The intoxicating chemical in marijuana is tetrahydracannabinol, or THC. According to research from the , the average THC content of marijuana has soared from less than 1 percent in 1972, to 3 to 4 percent in the 1990s, to nearly 13 percent in 2010. Today, some retail marijuana has 30 percent THC or more. The increased potency makes it difficult to determine the short- and long-term effects of marijuana
Cocaine acts by blocking the reuptake of certain neurotransmitters such as dopamine, norepinephrine, and serotonin. By binding to the transporters that normally remove the excess of these neurotransmitters from the synaptic gap, cocaine prevents them from being reabsorbed by the neurons that released them and thus increases their concentration in the synapses (see animation). As a result, the natural effect of dopamine on the post-synaptic neurons is amplified. The group of neurons thus modified produces much more dependency (from dopamine), feelings of confidence (from serotonin), and energy (from norepinephrine) typically experienced by people who take cocaine.
In addition, because the norepinephrine neurons in the locus coeruleus project their axons into all the main structures of the forebrain, the powerful overall effect of cocaine can be readily understood.
In chronic cocaine consumers, the brain comes to rely on this exogenous drug to maintain the high degree of pleasure associated with the artificially elevated levels of some neurotransmitters in its reward circuits. The postsynaptic membrane can even adapt so much to these high dopamine levels that it actually manufactures new receptors. The resulting increased sensitivity produces depression and cravings if cocaine consumption ceases and dopamine levels return to normal.
Dependency on cocaine is thus closely related to its effect on the neurons of the reward circuit.
The Science of Addiction: Genetics and the Brain
Nearly 15% of all men and 30% of all women admit to a craving for chocolate.
Over 300 substances have been identified in chocolate. Some of these, including caffeine and theobromine (another, less powerful stimulant) could actually cause dependency effects. But the amounts of these substances in chocolate are too small to really have any effect.
The same goes for phenylethylamine, a substance related to a family of stimulants called amphetamines. For example, chocolate contains less phenylethylamine than goat cheese.
Anandamide, a neurotransmitter produced naturally by the brain, has also been isolated in chocolate. The neural receptors for anandamide are the same ones to which THC, the main active ingredient in cannabis, binds. The anandamide in chocolate might therefore contribute to the feeling of well-being reported by “chocoholics” (though you would have to eat well over 30 kilos of chocolate to experience effects comparable to one dose of cannabis!).
Be that as it may, many scientists agree that dependency on chocolate could simply be due to its taste, which causes a sensation of intense pleasure that people want to repeat.