Substance and drug abuse can have serious negative effects on the body. Drugs are chemicals that work in predictable patterns to mimic, facilitate, or antagonize the body's normal functions, with their effects depending on factors like the substance, route of administration, dosage, and frequency of use. Common drugs of abuse include alcohol, tobacco, over-the-counter medications, depressants, narcotics, stimulants, and hallucinogens, each of which can impact the body in harmful ways when misused or abused.