What are the risk factors for developing an adverse drug reaction?

B is the correct choice because older age and organ impairment are well-established risk factors for developing adverse drug reactions (ADRs). As individuals age, the physiological changes that occur can significantly affect drug metabolism and clearance. This can lead to increased sensitivity to medications and a higher likelihood of experiencing ADRs.

Additionally, organ impairment, such as reduced kidney or liver function, can further complicate the pharmacokinetics of drugs, meaning that the body is either unable to adequately eliminate the drug or it processes it differently than in healthy individuals. This can result in drug accumulation and heightened effects, increasing the potential for adverse reactions.

In contrast, other options do not align as well with the recognized risk factors for ADRs. Young age and single medication use do not typically present a high risk for ADRs compared to the vulnerabilities associated with older age or multiple medications. High physical activity and a balanced diet generally contribute to overall health and do not directly correlate with increased adverse drug reactions. Similarly, a previous successful drug history does not indicate a reduced risk for ADRs, as individual responses to medications can change over time.