What is a known caution with phentermine due to its mechanism?

• A. Hepatic failure risk
• B. Dose-dependent CNS/BP adverse effects
• C. Hair loss
• D. Renal stones

Answer: (B)

Phentermine is a stimulant-like appetite suppressant that increases norepinephrine release in the central nervous system, boosting sympathetic activity to curb hunger. This mechanism explains why adverse effects are dose-dependent and primarily involve the central nervous system and cardiovascular system. As the dose rises, you’re more likely to experience CNS stimulation such as insomnia, agitation, and anxiety, along with cardiovascular effects like increased heart rate and higher blood pressure. That’s why a key caution with phentermine is to monitor for CNS stimulation and BP changes and to avoid use in patients with hypertension, tachycardia, or other cardiovascular risks. The other listed issues—hepatic failure, hair loss, and renal stones—are not characteristic cautions tied to its mechanism.