Toxicity studies are a critical component of drug development and regulatory affairs, designed to assess the safety profile of pharmaceutical compounds before they are approved for human use. These studies evaluate the adverse effects a drug may have on living organisms and help determine safe dosage ranges. Toxicity testing encompasses multiple approaches, varying in duration, species tested, and the endpoints measured. Regulatory authorities such as the FDA, EMA, and ICH provide detailed guidelines on conducting these studies to ensure the safety and efficacy of drugs. Toxicity studies can be broadly classified based on the duration of exposure, type of test organism, and the nature of toxic effects being investigated. Acute toxicity studies involve single or short-term exposure to determine immediate harmful effects, usually within 24 hours to 14 days. Sub-acute or sub-chronic studies examine repeated exposure over weeks to months to observe cumulative toxic effects. Chronic toxicity studies focus on long-term exposure, often extending for months to years, to detect delayed toxic