Drugs such as cocaine, amphetamines, methamphetamine, and opiates can cause a neurochemical reaction that significantly increases the amount of dopamine released by neurons in the brain's reward center. This rush of dopamine causes a burst of euphoria, or the “high”, that occurs when illicit drugs are abused. Usually, when something makes a person feel happy, a signal is sent to the VTA (ventral tegmental area) that travels to the nucleus accumbens and then to the prefrontal cortex, explains the National Institute on Drug Abuse (NIDA).Stimulants such as cocaine, amphetamines and methamphetamine stimulate the overproduction of neurotransmitters and can also prevent them from being reabsorbed normally, causing a large number of these chemical messengers to be present in the brain at the same time. This largely satisfies your natural reward system.
But repeated drug use also increases the threshold for this type of pleasure. This means you need to take more to get the same dose. Meanwhile, medications make your body less able to produce dopamine naturally. This leads to low emotional levels when you're sober. Many of the side effects of drugs on brain chemistry can be reversed when drugs are processed outside the body after a period of time.
However, some medications may have a longer lasting effect. Drugs such as methamphetamine can damage up to half of the dopamine-producing cells (and perhaps even more of the serotonin-containing nerve cells) in the brain with chronic exposure, warns the Drug Enforcement Administration (DEA). This damage may only be partially reversible, since chronic methamphetamine users may suffer from memory problems, learning problems, psychosis, aggression, emotional dysfunction and even develop Parkinson's disease as a result of functional and structural changes in the brain that may persist for years after they stop using it, reports NIDA. Different drugs may leave the body over varying amounts of time, and side effects can vary significantly in intensity during detoxification. Drug addiction sets in and people may feel compelled to continue using drugs to avoid these negative physical and emotional withdrawal symptoms. The American Society for Addiction Medicine (ASAM) defines addiction not only as a behavioral disorder, but also as a brain disease that affects brain chemistry and circuits and causes compulsive drug-seeking and consuming behaviors that interfere with daily functioning. Once the brain has become unbalanced due to drug abuse and dependence, it can take some time and effort to restore things.
When there is an addiction, dopamine, serotonin, and other neurotransmitters affected by drug abuse may no longer be produced, transmitted, or absorbed in the way they were produced before the introduction of drugs. Because many medications interact with it, it's important for your doctor to know all the medications you take. A high level of drug addiction, co-occurring medical or mental health disorders, polydrug abuse, a family history of addiction, high levels of stress, the experience of trauma, and a low level of support at home can contribute to the onset of addiction. Drugs can hijack the normal functions of these important brain chemicals, interrupt their communication and inhibit their functioning. When drugs aren't active in the brain, dopamine levels can drop, leading to uncomfortable withdrawal symptoms and severe cravings. Therefore, given the varied vision of researchers, one way to classify addictive drugs is to ask panels of experts.
It can be very pleasant, and people usually want to repeat the feeling with recurrent drug use.