Which term describes a decreased effect of a drug over time, leading to the need for larger doses?

Tolerance refers to the phenomenon where a person's response to a drug diminishes over time, resulting in the need for increased doses to achieve the same therapeutic effect. This occurs because the body may adapt to the presence of the drug through various mechanisms, such as increased metabolic activity or changes in receptor sensitivity. As a result, what was once an effective dose becomes insufficient, necessitating higher doses to maintain efficacy.

The other terms listed have different meanings. Synergism refers to the interaction between two or more drugs that produce an effect greater than the sum of their individual effects. Contraindication indicates a specific situation or condition in which a drug should not be used due to the risk of harm. Toxicology is the study of the adverse effects of drugs and poisons. These concepts do not relate to the gradual decrease in the effectiveness of a drug that characterizes tolerance.