Which factors influence a person's response to medication?

• A. Height, eye color, hair color, ethnicity
• B. Age, weight, gender, physical condition
• C. Diet, sleep, exercise, mood
• D. Weather, season, time since waking

Answer: (B)

Medication response varies between people because individual bodies handle drugs differently, influencing how a drug is absorbed, distributed, metabolized, and excreted, as well as how strongly a person responds to it. The factors that most impact this are age, weight, gender, and overall physical condition.

Age changes how organs function and how quickly drugs are processed—children may require different dosing than adults, and older adults often metabolize drugs more slowly or have reduced kidney function. Weight affects the amount of drug needed to reach a therapeutic level and how widely the drug distributes in the body. Gender can influence drug effects through differences in body composition, hormone levels, and enzyme activity, which can alter both how a drug is processed and its impact. Physical condition, including liver and kidney health and the presence of other illnesses, shapes metabolism and excretion, changing both the drug's duration and intensity of action.

Other factors like height, eye color, hair color, or ethnicity aren’t routinely used to guide dosing in everyday practice, though certain genetic or cultural considerations can matter for specific drugs. Diet, sleep, exercise, and mood can have secondary effects, such as altering absorption or adherence, but they are not primary determinants of how a drug works. Weather, season, or time since waking don’t directly determine a drug’s effect.

So, age, weight, gender, and physical condition best explain why different people may respond differently to the same medication.