In the field of Drugs Regulatory Affairs, toxicity studies are essential components of preclinical drug development, providing critical information about the safety profile of a new drug candidate. These studies are designed to evaluate the potential harmful effects of drugs on biological systems and guide the establishment of safe dosage ranges for humans. Toxicity studies are broadly categorized based on the duration of exposure, the type of toxic effects investigated, and the biological systems involved. They are governed by international regulatory guidelines such as ICH (International Council for Harmonisation) M3(R2), OECD (Organisation for Economic Co-operation and Development) guidelines, and country-specific frameworks like the US FDA and CDSCO (Central Drugs Standard Control Organization) regulations in India. Acute toxicity studies are the first step in evaluating a drug's safety. These studies involve the administration of a single dose or multiple doses within 24 hours to animals, typically rodents, to determine the immediate toxic effects and the median lethal dose (LD50). The primary goal is to observe the onset of toxicity, target organ effects, clinical signs, and mortality. Acute toxicity data help in selecting starting doses for sub-acute and chronic studies and in identifying potential emergency toxic reactions. Sub-acute or repeated dose toxicity studies involve the administration of the drug over a period ranging from 14 to 28 days. These studies are performed in at least two species (one rodent and one non-rodent) and are designed to evaluate cumulative toxicity, dose-response relationships, and reversibility of toxic effects. Parameters such as body weight, food consumption, hematology, clinical biochemistry, organ weights, and histopathology are monitored to identify target organs and systemic effects. Chronic toxicity or long-term toxicity studies assess the effects of prolonged exposure, typically 90 days to 6 months or longer, depending on the therapeutic indication. These studies provide data on potential cumulative organ toxicity, carcinogenic potential, and systemic alterations over extended periods. Chronic toxicity studies are critical for drugs intended for long-term use, helping regulators understand long-term safety implications before initiating clinical trials. Special toxicity studies include reproductive toxicity, genotoxicity, carcinogenicity, and immunotoxicity assessments. Reproductive toxicity studies evaluate the