**5.2.** *Chronic* **toxicity**

Chronic exposure refers to the administration of a toxin over an extended period of time, usually measured in months or years; this can cause irreversible toxicity. Periods between acute and chronic exposure could be referred to as subacute or subchronic. The results of chronic and acute toxicological studies help in the evaluation of any possible hazardous effect of a new drug or a drug which is in use with little or no documentation of its systemic toxicity.
