Maximum tolerated dose (MTD)

The highest dose of a medicine or treatment that will produce the desired effect without resulting in unacceptable side effects.

Higher concentrations of a drug are more likely to be effective but may induce side effects that deter use or outweigh the benefits of treatment.

Maximum tolerated doses are usually determined in animal studies and provide the basis for choosing the range of drug concentrations tested in phase 1 trials (dose escalation).

Guidance for Industry: M3(R2) Nonclinical Safety Studies for the Conduct of Human Clinical Trials and Marketing Authorization for Pharmaceuticals (FDA, 2010)