When a person uses drugs, it has significant effects on her brain. Recreational drugs, such as opioids, affect neurotransmitters in the brain. For example, the Canadian Institutes of Health Research and the Canadian Institute of Neurosciences, Mental Health and Addiction explain that when a person uses an opioid, such as heroin, the drug binds to receptors in the brain that endorphins and other opiate-like substances produced by the user's body normally bind to. Opioids also interfere with another neurotransmitter, GABA, which in turn increases the level of dopamine, a neurotransmitter that results in the euphoric feeling.
Other illegal drugs also affect the brain. Another example is amphetamines. The Canadian Institutes of Health Research and the Canadian Institute of Neurosciences, Mental Health and Addiction point out that amphetamines resemble the structure of dopamine, so when someone uses amphetamine, the drug pushes out stored dopamine, causing the brain to use the neurotransmitter.
But how does drug addiction affect someone in the long-term? When someone continues to use a drug, it can cause changes to the brain. The National Institute on Drug Abuse explains that doctors can use positron emission tomography (PET) to see changes in the brain from drug use; for example, people addicted to methamphetamine or heroin had lower levels of a type of dopamine receptor called the D2 receptor. As a person uses more of the drug, she built up a tolerance, meaning she needs to use more of the drug to get the same high as before.
In a new study funded by the National Institute on Drug Abuse, the researchers note that a regulatory protein may indicate if a person will become addicted to a drug, in particular cocaine. When a person uses cocaine, the drug blocks the recycling of three neurotransmitters: serotonin, norepinephrine and dopamine. The regulatory protein in question is MeCP2, which the researchers studied in rats. The press release from the National Institutes of Health explains that the same research group, Scripps Research Institute, also found a regulatory molecule called miRNA-212, which plays a role in cocaine use as well. The study found that MeCP2 and miRNA-212 regulated the intake of cocaine, but when there was a shift toward the MeCP2, the rats used more cocaine. As the researchers point out, this study could indicate how a person becomes vulnerable to drug use. Paul J. Kenny, the senior author of the study, notes that further research could find better treatments for cocaine addiction.