Phentermine HCl Capsules

Phentermine HCl is a prescription sympathomimetic amine anorectic used short-term as part of the management of exogenous obesity. It acts by suppressing appetite and stimulating the central nervous system in a manner similar to amphetamine-class drugs. Initially introduced in 1959, phentermine in its hydrochloride form has been used since the 1970s for weight-loss therapy.^[1] It is intended for individuals with obesity, typically defined as a BMI of ≥ 30 kg/m² or ≥ 27 kg/m² with weight-related comorbidities, and is prescribed alongside dietary modifications and exercise. A valid prescription is necessary, and phentermine is classified as a Schedule IV controlled substance due to its potential for abuse and dependence.^[2]

Phentermine maintains a long-standing record in obesity treatment, receiving FDA approval as a resin complex in 1959 and then as a hydrochloride salt in 1973 for short-term weight management.^[1] In the mid-1990s, it was infamously combined with fenfluramine (“Fen-Phen”), which was linked to cardiac valvular disease and pulmonary hypertension. These adverse outcomes were attributed to the serotonergic properties of fenfluramine, leading to its market withdrawal in 1997.^[3] When used alone at recommended doses, phentermine has not been associated with such valvular or pulmonary complications, since it lacks direct agonism at the 5-HT₂B receptors implicated in fenfluramine’s toxicity.

Phentermine remains widely prescribed by itself for short courses, and in 2012 it was FDA-approved in combination with topiramate for chronic weight management. However, phentermine monotherapy remains indicated only for relatively brief use (several weeks up to 12 weeks) and is discontinued thereafter to mitigate tolerance and side effects.^[1] Treatment should always be overseen by a qualified healthcare provider, with concurrent attention to diet, exercise, and behavioral strategies to support lasting weight loss.