What is drug tolerance?

The word tolerance means the ability to endure a condition without any adverse reactions. When we are subjected to unfavourable situations over and over, we develop a tolerance for it. Eventually, the effect of those situations on us reduces. This phenomenon also happens with most addictive substances. 

Think about the first time you consumed alcohol. You could probably feel the effect immediately after your first drink. But after a while, you need to drink more and more to achieve the same effect. It is the same with caffeine or any other substances. Our body’s response to these drugs is reduced over time. This is our body’s way of coping with the changes brought in by the drugs. 

In simple words, drug tolerance is what happens when your brain does not respond to a drug the way it used to. As a result, people take larger quantities of the substance to achieve the same high. This tolerance is also likely to reduce as drug use is reduced. 

Is tolerance the same as dependence? 

The term tolerance is often confused with drug dependence or addiction. In the case of drug dependence, the body experiences withdrawal symptoms in the absence of the drug. However, in drug tolerance, the body just stops responding the way it once used to, to the particular drug. Having developed tolerance for a substance does not mean that one is addicted to it. However, it increased the risk of getting addicted. 

How does tolerance develop?

Tolerance develops when one takes a drug repeatedly. It could be a prescribed drug or a recreational one; a high tolerance might develop after regular use. Studies show that it can also be genetic. If your parents had a high tolerance for drugs, it is possible that you might too. There are certain other factors that determine how fast one develops tolerance. For example, body weight, gender or age. 

Drug tolerance happens on two levels: physiological and behavioural. On a physiological level, there might be changes in the receptors or enzymes that react with the substance. For example, the liver might produce larger quantities of enzymes called alcohol dehydrogenase that break down alcohol. It breaks it down to acetic acid. Lessening the duration and extent of the effect. 

Behavioural tolerance is psychological. On repetitive use, one might not feel the effect of the drug they used. This could be due to associations with certain settings or conditions. Once familiar with the effects of the drug, they might compensate and behave like they haven’t used the drug. 

Types of tolerance

Tolerance refers to the level at which the substance starts to show an effect on your body. This tolerance can be seen in various different ways. In some cases, tolerance can be seen in a single use within minutes of consumption. This is known as acute tolerance. 

Alcohol tolerance

Alcohol tolerance can either be environment dependent in which your tolerance level changes based on where you are, for example, in a bar vs at home. Or it can be environment-independent, in which case there might be other factors altering the tolerance, like on a neuronal level. 

Once one is aware of the effects of the substance on one’s behaviour, it is possible to learn to manage that effect. This is called learned tolerance, where one might change their behaviour in order to cope with the effect of alcohol. The most common form of tolerance in the case of alcohol is metabolic tolerance. The body starts to metabolise alcohol faster, reducing its effect on the body. 

Drug Tolerance

With most prescription and recreational drugs, metabolic tolerance develops where the concentration of the drug in the brain reduces over time. Another type is pharmacodynamic tolerance. In this case, either there are changes in the receptor binding or the body enables processes that reduce the effect of this binding with receptors. Another common term in this area is tachyphylaxis. In this case, one might develop a low response with over-exposure to the same drug over a period of time. 

Why is drug tolerance dangerous?

Drug tolerance may develop with prescription drugs or recreational drugs. As one feels lesser effects of the substance or drug, they may seek larger quantities to achieve the same effect. This increases the risk of drug abuse and addiction. And although the effect of these drugs may seem to have been reduced, higher doses of the substance will continue to damage the body in different ways. 

Although it might feel like a positive thing that the drugs don’t seem to be affecting the body the same way, this is often misleading. Having a high tolerance can put one at risk for addiction, sexual problems, High BP, and cancer. On becoming aware of this increasing tolerance, people often end up taking more substances than intended. They might even mix different substances to achieve a different kind of effect. This increases the chances of overdose. 

What can you do?

You might be at risk of developing a high tolerance if:

• You consume alcohol or other drugs frequently
• You have a history of family alcohol or drug use
• You have a history of mental health issues
• Show patterns of binge drinking commonly seen in college students

As mentioned earlier, as tolerance increases with regular substance use, it also decreases as exposure to alcohol or drugs reduces. You can hence reduce your tolerance by cutting down or completely stopping the use of the particular substance. However, it is best to seek professional help because there might be chances of developing withdrawal symptoms. 

If you or someone you know is developing a high drug tolerance, then you might be at risk for alcohol or drug use disorders. It is best to seek help at this stage. Reach out to a professional through our list of treatment centres here. 

Sources

Huizen, J. (2022, March 28). What to know about drug tolerance. Medical News Today. https://www.medicalnewstoday.com/articles/drug-tolerance

Melchior, C. L., & Tabakoff, B. (1985). Features of environment-dependent tolerance to ethanol. Psychopharmacology, 87(1), 94–100. https://doi.org/10.1007/BF00431786 

Negus, S. S., Selley, D. E., & Sim-Selley, L. J. (2010). Pharmacodynamic tolerance. Encyclopedia of Psychopharmacology. Springer-Verlag, 994-997. https://doi.org/10.1007/978-3-540-68706-1_272 

Pietrzykowski, A. Z., & Treistman, S. N. (2008). The molecular basis of tolerance. Alcohol research & health : the journal of the National Institute on Alcohol Abuse and Alcoholism, 31(4), 298–309. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3860466/ 

Webb, N. (2011). Tachyphylaxis. In: Kreutzer, J.S., DeLuca, J., Caplan, B. (eds) Encyclopedia of Clinical Neuropsychology. Springer, New York, NY. https://doi.org/10.1007/978-0-387-79948-3_1752