Drug Tolerance Explained

toleranceOur brain thrives on novelty and dopamine helps us store information about novel situations.  We know that dopamine is released when we receive a reward, but it is also involved in noting unexpected rewards. If you get more juice than you anticipated, your brain releases dopamine and sends it to the anterior cingulate in your frontal cortex, a brain region responsible for anticipating rewards and making decisions. Get less juice than you anticipated and, again, your brain will encode the information, but this time, by sending less dopamine to the anterior cingulate. If you get the same amount of juice you expected, no dopamine is released. This mechanism enables us to recognize patterns and learn which behaviors lead to risk versus reward.

How does this translate into drug and behavioral tolerance? When you use cocaine for the first time, your brain registers it as a pleasurable experience. After using it a few more times, you might notice that you don’t experience the same level of euphoria as before. That’s because the experience has lost novelty and your brain has learned to recognize the pattern. In other words, dopamine isn’t released since there isn’t anything novel about the experience. Tolerance is born. In order to achieve euphoria from cocaine, you must now use more.

The same process occurs with compulsive behaviors. The first few times you shoplift (and don’t get caught) you experience relief and pleasure, but with subsequent trials you notice a decrease in the euphoria you experience. So, you start shoplifting more frequently.

NoteThere are many neurobiological mechanisms at play in addiction and compulsive behaviors and the role of dopamine in addiction and tolerance is just one facet of a complex biopsychosocial phenomenon.

This is your brain on dopamine

Dopamine_PathwaysDopamine is a neurotransmitter responsible for movement, pleasure, motivation, and cognitive processes, such as learning. For the purposes of understanding its role in addiction, let’s concentrate on pleasure and motivation.

Whenever we do something that propagates the advancement of our species, dopamine is released in order to motivate repetition of the action. When we sleep, eat, and have sex dopamine is released in our brain and the message is, “That was great, do it again!” We also release dopamine whenever we find something pleasurable. Be it 18th century poetry, heroin, or Radiohead, our brain will release dopamine to encode the stimulus as something that brings us pleasure.

Dopamine not only serves to categorize the good things we encounter in life, it also programs our pre-frontal cortex (the part of the brain involved in judgement and decision making) to alert us when the pleasurable stimulus is available. If your brain cells could talk, it might sound something like, “OMG! There’s a flyer on that lamppost for a Radiohead concert. Go look at it!” In other words, we become hyperaware of opportunities for engaging in behaviors that bring us pleasure. In fact, a study on people with alcoholism found they were more likely to spot alcoholic beverages in a busy photograph than people who don’t have problems with alcohol.

When we consume substances, it makes us feel good because our brains release dopamine, but drugs elicit a higher amount of dopamine release than is necessary. This is part of what causes experiences of euphoria and feeling high. Sometimes the amount of dopamine released is so great, the chemicals in our brain become unbalanced and we may experience hangover or withdrawal. In time, our brain regains chemical equilibrium. However, if one abuses substances, the brain may develop a tolerance (meaning the person needs to use greater amounts to get high) or dependence on the substance as a source of dopamine. If one becomes dependent on a drug, it may take some time for the brain to regain equilibrium and the person may experience extreme physical discomfort and emotional distress when they aren’t using. The period of re-calibration depends on the amount, type, and frequency of the drug used. It’s always a good idea to be under medical supervision and receive support from friends, family, and a mental health professional if you’re dependent on a drug and want to stop or decrease your use.

The mechanism of tolerance is also evident in impulse control disorders, such as sex addiction, kleptomania, and compulsive gambling. Although it doesn’t appear that persons with an impulse control disorder undergo the same intensity of withdrawal that persons addicted to substances experience, there can certainly be a period of re-calibration of dopamine receptors during which a person feels irritable and agitated after stopping a behavior.

Based on the information presented here, it appears that we are all hard-wired to become addicts and you may be asking yourself, “If this is true, why do some people become addicted and others don’t?” This is a really good question and the answer is “We don’t really know.” We can predict the likelihood of someone becoming an addict based on factors such as first age of substance use and family history of addiction, and we know that a lack of social support and coping strategies (especially when coupled with mental illness) can also lead to addiction, but there is no conclusive answer to date.

The best ways to prevent addiction are to educate yourself about the substances you use (or to abstain from substance use altogether) and to be mindful about the choices you make. If you have a mental illness, ensuring that you are getting appropriate treatment and maintaining social support are good preventative measures.