Drugs, encompassing various chemical compounds from natural sources, lab synthesis, or genetic engineering, elicit different biological responses in living organisms. Some of these responses are desirable or therapeutic, while others are undesirable. The primary goal of administering a drug is to achieve a therapeutic effect, that is, to address a specific disease or health condition. Any concurrent effects outside of this therapeutic outcome are considered undesirable. These undesirable effects fall into two categories: side effects and toxic effects. Side effects, although unwanted, are an inevitable part of a drug's pharmacodynamic action. They are generally not harmful but can cause discomfort. For example, atropine, used to reduce mucus production, can unintentionally cause dry mouth due to its primary mechanism of action. On the other hand, toxic effects are harmful and can be grouped into pharmacological, pathological, or genotoxic effects. Pharmacological toxicity often results from overuse or prolonged consumption of a drug. It usually subsides once the drug is metabolized or excreted, reducing its concentration in the body. Pathological and genotoxic effects can be reversed, but some severe cases may lead to serious health problems like cancer or death.