The human brain is only three pounds of gray and white matter, but it’s the most complicated organ in your body. It’s the center of everything you do and think. It operates your whole body — your every function, voluntary and involuntary. In short, your brain is you.
You’d need a whole new degree to completely understand how the brain works, but there are a few basics that will help you understand how drugs affect the function of the brain. The brain is structured roughly like a computer chip, with billions of interconnected cells called neurons. Neurons act as switches, sending and receiving electrical signals to each other and to the rest of the body.
These signals are triggered by neurotransmitters, specific chemicals that travel between neurons through gaps called synapses. Those neurotransmitters are a specific shape and fit into their receptors like a key into a lock.
Drugs interfere with the natural function of the brain in a number of ways. Some drugs, like marijuana and heroin, mimic the natural neurotransmitters that the brain produces, allowing them to fit in the neurons. Although chemically, these compounds are similar to the body’s natural neurotransmitters, they don’t interact with neurons in the same way.
Other substances, like amphetamine and cocaine, can cause neurons to release abnormally large amounts of certain neurotransmitters, interfering with normal communications in the brain. They can also prevent the normal recycling process — the means by which neurotransmitters are sent back to the cells they started in so they can be used again.
Depending on the area most affected, drugs can have drastically different effects and long-term consequences for the brain, including a lasting effect on life-sustaining functions.
The basal ganglia is the part of the brain associated with developing habits and routines. It’s the part of the brain that causes the subjective experience of pleasure associated with eating, socializing, and sex, and is thus often referred to as the brain’s “reward circuit.”
Drugs activate this circuit to a much greater degree than natural stimuli, causing extreme senses of pleasure — the problem is that over repeated exposure, the “reward circuit” starts to adapt to the drug. Eventually, it loses its sensitivity so much that natural stimuli don’t trigger it anymore, leading to a dependence on the drug to replicate those sensations.
The extended amygdala is the part of the brain that contributes to stressful feelings like anxiety, irritability, and unease. Normally, these features are useful in getting us out of bad situations — they’re sort of a defense mechanism for the mind.
The problem is that the extended amygdala also contributes to withdrawal symptoms when drug usage fades, prompting the user to seek out the drug again. This mechanism gets more sensitive over time — the “lows” get “lower” and the “highs” don’t get any “higher.” Eventually, the person with the substance misuse disorder starts to use the drug just to avoid the discomfort, not to get high.
The prefrontal cortex is the portion of the brain that affects rational decision-making. It powers thinking, planning, problem-solving, and self-control. This is also the last portion of the brain to mature as people get older, making it especially vulnerable in teens and young adults.
As the balance between the circuits for reward and stress in the basal ganglia and extended amygdala become disrupted by drug use, it also disrupts the prefrontal cortex, reducing their impulse control and causing them to seek the substance compulsively. This mechanism is the root of addiction.
Of course, some drugs also have further physiological effects that start in the brain — pupil dilation, elevated heart rate, increased energy, and effects on breathing and sleeping all trace their roots to various parts of the brain, which is what allows drugs to do so much physical damage and even cause death.
The high from drugs is complex and not well understood, but seems to be tied to an increase in the brain’s production of endorphins and other neurotransmitters. These chemicals do occur naturally in the brain in response to eating, music, sex, creative pursuits, social interaction, and other stimuli, but drugs can produce far greater amounts of these compounds.
It was once thought that dopamine itself — a neurotransmitter in the brain — caused euphoria and the experience of a “high” by itself, but that’s no longer thought to be the case. Current research now indicates that dopamine has more to do with causing us to repeat the activities we find pleasurable, building habits and reinforcement, than with the sensation of pleasure itself.
When the reward circuit in the basal ganglia is activated by a source of pleasure, a release of dopamine tells is that the experience was positive and should be sought out again. The more often this happens, the less we have to focus on remembering to seek out that experience — it becomes habitual.
Just as drugs produce an intense euphoria, or “high,” they also produce an unnaturally large surge of dopamine. This reinforces the association between the pleasure and the drug in a powerful way, making it more likely that the user will seek out the drug again and again to reproduce that euphoria.
These peaks in dopamine, as with any other source of dopamine, also become associated with the environment in which drug use occurs. Certain locations, people, smells, sights, and other impulses can trigger cravings in people to use drugs again, making new habits a vital part of any substance recovery plan.
The brain mechanism for natural rewards versus those that come from drugs isn’t really different — the same chemicals are released, the same areas of the brain are triggered. So why is cocaine, for example, so much more addictive than riding a bike?
Think of the difference like the difference between loud and soft noises. If your speakers only produce loud noises, eventually you’ll turn them down. If a soft noise then comes out of the speakers, you won’t hear it.
The problem with drugs isn’t the type of chemical reaction it produces in the brain, it’s the magnitude. When the brain experiences the massive spikes in pleasure and dopamine that drugs produce, it becomes less sensitive — turning down the volume, as it were, on its response to those compounds.
This is why a person who develops a substance misuse disorder starts to feel flat, unmotivated, and lifeless — the natural sources of pleasure and dopamine in their lives can no longer compete with the huge spikes that drugs afford them.
Luckily, the brain can be “re-tuned.” With a good recovery program and medication, the brain will re-calibrate to more natural levels of dopamine and pleasure to the point that it no longer requires drugs to sustain its function. If you or a loved one has a problem with substance misuse, it’s never too early — or too late — to seek help.