subchronic

Subchronic is a term used in toxicology and pharmacology to describe exposure or effects that occur over a duration longer than an acute exposure but shorter than a chronic one. In practice, subchronic exposure typically refers to repeated exposure over weeks to months, with 90 days (about three months) being a standard duration for many animal toxicity studies. Subchronic studies are designed to identify adverse effects that may not appear after a single dose and to characterize dose–response relationships over a medium-term period.

These studies commonly involve repeated dosing of a substance to laboratory animals such as rats or mice, and sometimes non-rodents, followed by monitoring of clinical observations, body weight and food consumption, hematology and clinical chemistry, organ weights, and microscopic examination of tissues. The goal is to determine target organs, the lowest-observed-adverse-effect level and the no-observed-adverse-effect level, and to establish a basis for risk assessment and regulatory limits.

Subchronic exposure is distinguished from acute exposure (a single or short-term exposure with immediate effects) and chronic exposure (long-term exposure, often months to years, with potential cumulative toxicity). The term may also be used in medical and occupational contexts to describe repeated exposures of intermediate duration in humans.

Limitations include that subchronic findings do not always predict chronic effects, and extrapolation across species and to humans introduces uncertainty requiring safety factors in risk assessment.