Adulteration of drugs refers to the act of intentionally or unintentionally contaminating, substituting, or altering pharmaceutical products, resulting in a reduction of quality, efficacy, or safety. In the context of epidemiology and clinical trials, drug adulteration is a critical concern because it can compromise the validity of clinical study outcomes, mislead therapeutic efficacy evaluations, and pose significant public health risks. Adulteration may lead to unpredictable pharmacological effects, adverse drug reactions, or therapeutic failures, which can distort epidemiological data and undermine evidence-based medicine. Regulatory authorities and clinical researchers rely on stringent quality control measures and analytical testing to detect and prevent adulteration to ensure patient safety and the reliability of clinical trials. Deliberate adulteration involves intentional modification of drugs for economic gain, enhanced effects, or other unethical purposes. It is distinct from accidental contamination, which occurs due to poor manufacturing practices or environmental factors. Several types of deliberate adulteration are commonly observed: 1. Substitution: This involves replacing a genuine drug with an inferior or entirely different substance. Substitution may occur when manufacturers use cheaper raw materials or counterfeit active ingredients to reduce costs. In clinical trials, substitution can compromise study outcomes, as the administered substance may not have the expected pharmacological action. 2.