Chronic toxicity studies are preclinical studies that are conducted to assess the potential adverse effects of a substance after repeated exposure over a period of several months to several years. These studies are usually conducted in laboratory animals, such as rats, mice, rabbits, or dogs, to evaluate the long-term safety of a drug or other substance before testing in humans.

The primary objective of chronic toxicity studies is to identify any potential toxic effects that may develop over a longer period of time after repeated exposure to the substance, including any effects on the organs, tissues, and systems of the body. These studies typically involve administering the test substance to the animals daily for a period of 6 months to 2 years, depending on the duration of exposure intended in human use.

The animals are monitored closely during the study period for any changes in behavior, clinical signs, body weight, food consumption, and organ function. At the end of the study period, the animals are sacrificed, and various tissues and organs are examined for any signs of toxicity, including histopathological examination.

The results of chronic toxicity studies can help determine the safety profile of the substance, including the no-observed-adverse-effect level (NOAEL) and the lowest-observed-adverse-effect level (LOAEL). The NOAEL is the highest dose of the substance at which no adverse effects are observed after long-term exposure, while the LOAEL is the lowest dose at which adverse effects are observed after long-term exposure.

Overall, chronic toxicity studies provide valuable information about the long-term safety of a substance and can help identify potential safety concerns that may need further investigation in clinical trials. These studies are an essential part of the preclinical safety assessment of drugs and other substances before testing in humans.