Who is at the highest risk for experiencing an adverse drug reaction?

The highest risk for experiencing an adverse drug reaction is typically seen in populations with increased physiological vulnerability, one of which is infants, particularly very young ones like a 3-month-old. Infants have immature liver and kidney function, which play crucial roles in drug metabolism and excretion. Their developing systems are not yet fully equipped to handle medications that adults or older children can process, making them more susceptible to both toxicity and adverse reactions.

Additionally, dosages for infants must be carefully calculated based on weight and developmental stage, further complicating drug administration. This population also lacks the ability to communicate side effects effectively, which can delay recognition and treatment of adverse reactions. Factors such as the greater likelihood of polypharmacy in older adults, as seen in the other choices, can lead to adverse effects, but the immature biological processes in a young infant pose a higher inherent risk.