Know the Facts

Helping you make informed decisions about your drinking

Tolerance

The term ‘tolerance’ refers to a person’s level of responsiveness to the effects of alcohol. Having a high tolerance to the effects of alcohol means that a person has to drink more and more to get the same effect that they used to get. There are two main ways in which people develop tolerance to the effects of alcohol.

Through metabolism

As a person drinks more and more, the liver gets more efficient at breaking down alcohol. This is because the level of the enzyme required to break down alcohol, alcohol dehydrogenase, increases slightly, allowing alcohol to be processed faster, and is also due to changes in the metabolic pathways in favour of more efficient processes. Because the liver becomes more efficient at processing the alcohol and removing it from the blood, it takes longer for blood alcohol concentration to rise and for the effects of the alcohol to be felt. This leads to the person drinking more and more to get the same effects they used to.

Over time, very heavy alcohol use can actually lead to reverse tolerance, where small amounts of alcohol can have very quick and strong effects. This is because the liver damage that tends to occur after long periods of heavy alcohol use reduces the liver’s ability to break down alcohol, resulting in very high blood alcohol concentrations.

Through changes in the central nervous system

The other way in which people become tolerant to the effects of alcohol is through changes that happen in the central nervous system (CNS). Alcohol acts in the CNS by changing the balance of neurotransmitters, which are chemicals that send messages between nerves. Alcohol reduces the effect of excitatory neurotransmitters, and increases the effect of inhibitory neurotransmitters, altering the natural balance of the nervous system.

If alcohol is consumed often, keeping the system off balance, the brain tries to fix this imbalance by increasing the activity of the excitatory neurotransmitters (which alcohol usually decreases) and decreasing the activity of the inhibitory neurotransmitters (which alcohol usually increases). This correction reduces the effect of the alcohol, meaning the same amount will have less effect than before. This leads to the person having to drink more to feel the effects they used to.

Sources

  • Forrest, E. & Reed, E. (2011). Alcohol and the liver. Medicine, 39, 532-535.
  • Schuckit, M.A. (2006). Drug and alcohol abuse: A clinical guide to diagnosis and treatment. New York: Springer Science+Business Media, Inc.
  • Valenzuela, C.F. (1997). Alcohol and neurotransmitter interactions. Alcohol Health and Research World, 21, 144-148.