Drug tolerance (or physiological tolerance) is a term used to describe that the organism gets used to a given substance. Drug tolerance also means that over time a drug becomes less effective and larger amounts of the substance are needed to get the same effect.
Physiological tolerance can be achieved in one of the following ways:
- By changing the number of receptors for a substance
- By changing the way the signal is handled
- By changing the receptors themselves
- By changing the system that antagonizes the receptor