A tolerance to a substance occurs when the body gets used to a substance (drugs, alcohol or medication) so that more of the same substance is needed to give the desired effect that was once received initially from smaller amounts.
There are several mechanisms behind tolerance, including changes in the metabolism of a drug, cellular changes or behavioural/psychological effects. Tolerance is not always negative, and people may develop a tolerance to the side effects of a drug over time as well.
We look at these issues and many others in this article. This is one not to miss if you think that you or someone else you know may have developed a tolerance to medications or substances.