The psychoactive constituent of cannabis, delta-9 THC, affects the brain in a fundamentally different way than many other drugs, such as cocaine and opiates. These drugs are associated with the dopamine pathways within the brain and are subject to high rates of abuse, as seen with self-administration experiments done with animals. Early research on cannabis' effects on the brain was limited by the technology of the time and was thus subject to influence by observations of behavior, rather than neuropharmacology. This lack of concrete knowledge about THC's effects allowed cultural biases to maintain fallacy that marijuana acted similarly to heroin. Research done during the past decade, since the discovery of a THC receptor in the brain, has refuted such claims.
Dopamine is a neurotransmitter in the brain that is associated with pleasure.
These systems are intimately involved with limbic system, an area of the brain which is associated with the control of emotions and behavior. Highly addictive drugs, such as cocaine, affect these pathways and cause an effective increase in the amount of dopamine in the brain. Cocaine and amphetamines block the reabsorbtion of dopamine, thus prolonging and intensifying the effects. Opiates activate production of dopamine by blocking the inhibitory signal, gamma-aminobutyric acid, which would ordinarily slow or stop dopamine production. Research on animals and observations of addicts in our population has shown that animals will forsake their own personal good, whether it be refusing food and water or exposing themselves to extreme risk of contracting HIV, in order to stimulate the brain's reward system.