Final answer:
The correct answer is B) Unintended secondary effects, which are effects of a drug that are not the main intended physiological response. Side effects may vary based on several factors, including dosage, route of administration, and individual patient response to a medication.
Step-by-step explanation:
The best definition for a side effect is B) Unintended secondary effects. A side effect refers to any unintended and typically undesired effects that accompany the primary purpose of the drug. Although medication is given to achieve a certain physiological response, there can sometimes be additional effects that are not the main aim of the medication. These unintended effects can be minor or severe, and they may appear immediately upon taking the medication or only after long-term use. It's essential to understand that side effects can affect various systems within the body and result from changes in specific biochemicals. Factors like the dosage and route of administration influence the likelihood and severity of side effects. For instance, common side effects of antidepressants can include dizziness, weight gain, or insomnia, among others. It is also important to distinguish side effects from drug tolerance, which occurs when more of the drug is needed to experience the same effects, and from drug dependence, which is when cessation of drug use results in withdrawal symptoms.