Neurotransmitters are substances in your brain that pass between individual nerve cells and relay chemical signals that allow these cells to work together and support your body’s essential functions. Certain drugs and behaviors alter the ways in which your brain produces its neurotransmitters, or alter the ways in which your brain’s nerve cells (neurons) respond to the presence of various neurotransmitters. Addiction occurs when these alterations change your basic brain chemistry and force you to rely on specific drugs or behaviors in order to maintain a “normal” chemical environment.
The human brain contains a vast number of neurons that help control both voluntary and involuntary functions throughout your body. To achieve the degree of control required to keep you functioning properly, your brain needs a way to simultaneously coordinate the activities of large groups of neurons. Neurotransmitters, which are produced within the neurons themselves, provide this coordination by passing chemical signals between specific neuron groups. Since your brain needs to achieve a wide variety of goals at any given time, it relies on a wide range of neurotransmitting chemicals, including substances called dopamine, serotonin, acetylcholine, epinephrine and norepinephrine.
Each neuron in your brain produces neurotransmitters at one end of its structure and receives signals from other neurons’ neurotransmitters at its opposite end. The receiving end of the neuron contains sites, called receptors, which act as interfaces for specific neurotransmitters and allow those neurotransmitters to communicate with the cell. Unless a neurotransmitter finds its proper receptor, it can’t interact with the targeted neuron.
Neurotransmitters and Drug Effects
Drugs with a potential to produce abuse and addiction have an effect on your body because they alter the neurochemical environment in your brain. Some drugs, such as heroin and marijuana, have chemical structures that closely mimic the structures of your neurotransmitters. These similarities give the drugs access to the chemical receptors on your neurons, and allow them to alter the signals that get passed on to other neurons. Other drugs, including methamphetamine and cocaine, achieve their effects by increasing your brain’s production of certain neurotransmitters, or by interfering with the way your brain recycles its neurotransmitters for future use.
The neurotransmitter dopamine plays a primary role in your brain’s response to the presence of various drugs of abuse, according to the National Institute on Drug Abuse. Normally, dopamine has responsibilities that include regulating your emotional responses, controlling the movements of your body and determining whether you perceive any given experience as painful or pleasurable. Simply stated, pain responses occur when your dopamine levels drop, and pleasure responses occur when your dopamine levels rise. Whatever specific interactions they have with your neurons, all drugs associated with abuse and addiction trigger significant increases in your brain’s dopamine output, and therefore produce feelings that you perceive as pleasurable.
The Onset of Addiction
Over time, use of drugs that increase your dopamine levels will force your brain to compensate and alter the ways that it processes this neurotransmitter. Depending on your specific circumstances, these alterations may include reduced dopamine production in your neurons, a reduction in the number of dopamine receptors on your neurons, or a combination of both of these effects. The overall result of these changes is a lower dopamine level. Since dopamine is responsible for sensations of pleasure in your body, a reduction in its presence will lead to painful mental states such as listlessness or depression, or a general feeling that you’re “not yourself.”
Addiction sets in when you start to rely on any given drug to restore your brain’s dopamine supply to the levels that existed before drug use began. Over time, addiction worsens when your brain develops a tolerance to a drug’s dopamine-boosting effects and you begin to require increasing amounts of the drug in order to maintain a “normal” chemical environment.
Addiction Without Drugs
Even without the use of drugs, your brain can develop neurotransmitter alterations that lead to the onset of addiction, the University of Pennsylvania Health System reports. These alterations occur when you have what psychiatrists call a “manic” reaction to certain activities and behaviors — such as shopping, having sex, eating, gambling or shoplifting — and seek to participate in them repetitively or compulsively. As in people with drug addictions, people with these behavioral addictions come to rely on their targeted activities in order to boost their levels of dopamine, as well as their levels of the neurotransmitter epinephrine (also known as adrenaline).
No one can predict exactly how much drug use will trigger the onset of addiction in any particular person. Similarly, no one can predict exactly who will develop a behavioral addiction. Specific factors that play a role in your susceptibility to addiction include your genetic makeup and details of your personality and ongoing daily environment. It’s basically impossible to accurately map out all of the possible interactions between these factors. In part for this reason, any use of a dopamine-altering drug can potentially lead to abuse and addiction. While appropriate treatment can control or reverse the short-term effects of drug or behavioral addiction, a recovering addict typically has lifelong heightened risks for the recurrence of drug use and/or addictive behaviors.