Phentermine Drug Class
Phentermine is a sympathomimetic amine anorectic (appetite suppressant) that functions as an adrenergic agonist. 1, 2, 3
Mechanism of Action
Phentermine works by activating the sympathetic nervous system through norepinephrine release, which leads to:
- Appetite suppression via hypothalamic stimulation
- Increased resting energy expenditure
- Decreased food intake
The drug has pharmacologic activity similar to amphetamines (d- and d/l-amphetamine), though it is not optically active like amphetamine itself 4, 5, 4, 3. It acts as a potent substrate at the norepinephrine transporter while promoting norepinephrine release, with weaker activity at the dopamine transporter and negligible activity at the serotonin transporter 6.
Classification Details
- Pharmacologic class: Sympathomimetic amine / Norepinephrine-releasing agent 2
- Therapeutic class: Anorectic or anorexigenic agent 3
- Controlled substance status: Schedule IV 1, 5, 3
- Chemical structure: α,α-dimethylphenethylamine hydrochloride (a phenethylamine derivative) 3
Regulatory Status
Phentermine was approved by the FDA in 1959 and remains the most commonly prescribed anti-obesity medication in the United States 4. It is approved only for short-term use (≤12 weeks) 1, 2, 5, though many practitioners prescribe it off-label for longer durations in clinical practice 4, 5, 7.
The Schedule IV classification reflects concerns about potential abuse and dependence, as phentermine is chemically and pharmacologically related to amphetamines 7, 3.