What is Phentermine (anorexiant medication)?

From the Guidelines

Phentermine is an adrenergic agonist that promotes weight loss by decreasing food intake and increasing resting energy expenditure, and it is the most commonly prescribed anti-obesity medication, typically prescribed as part of a comprehensive weight management program that includes diet and exercise. The medication works by activating the sympathetic nervous system, which leads to a decrease in hunger signals, and it is usually taken once daily in the morning before breakfast or 1-2 hours after breakfast, with common dosages ranging from 15-37.5 mg daily 1. Some key points to consider when prescribing phentermine include:

• It was approved by the FDA in 1959, but only for short-term use (3 months), although in clinical practice, many practitioners prescribe it for a longer duration 1
• In a 28-week, randomized, controlled trial, phentermine alone (15 mg daily) was associated with a 6.0-kg weight loss at 28 weeks, compared with a placebo 1
• The recommended dosage of phentermine is 15 to 37.5 mg orally once daily in the morning, and low-dose phentermine recently received FDA approval under the brand name Lomaira as a scored 8-mg tablet that can be prescribed up to 3 times per day 1
• Common side effects of phentermine include dry mouth, difficulty sleeping, dizziness, and irritability, and it should not be used with monoamine oxidase inhibitors or other sympathomimetic amines 1
• Appropriate candidates for phentermine include patients with obesity who need assistance with appetite suppression, but it is generally used in younger patients without evidence of active or unstable coronary disease, or uncontrolled hypertension 1.

From the FDA Drug Label

Phentermine hydrochloride is a sympathomimetic amine anorectic. Phentermine is a sympathomimetic amine with pharmacologic activity similar to the prototype drugs of this class used in obesity, amphetamine (d- and dll-amphetamine). Drugs of this class used in obesity are commonly known as “anorectics” or “anorexigenics. ” Phentermine is indicated as a short-term adjunct (a few weeks) in a regimen of weight reduction based on exercise, behavioral modification and caloric restriction in the management of exogenous obesity for patients with an initial body mass index greater than or equal to 30 kg/m 2, or greater than or equal to 27 kg/m 2 in the presence of other risk factors (e.g., controlled hypertension, diabetes, hyperlipidemia) 2, 2, 2.

• Key points:
  • Phentermine is a sympathomimetic amine anorectic
  • Used for short-term weight reduction
  • Indicated for exogenous obesity with a BMI ≥ 30 kg/m2 or ≥ 27 kg/m2 with other risk factors

From the Research

What is Phentermine

• Phentermine is an anti-obesity medication (AOM) used for weight loss in adults 3
• It is a dopaminergic appetite suppressant, which means it works by reducing hunger and increasing feelings of fullness 4
• Phentermine is often prescribed in combination with other medications, such as topiramate, to enhance its weight loss effects 5, 6, 7

Mechanism of Action

• Phentermine's exact mechanism of action is not fully understood, but it is thought to work by increasing the release of dopamine, a neurotransmitter that regulates appetite and satiety 4
• It may also affect other brain regions involved in appetite regulation, such as the nucleus accumbens shell (NAcSh) 4

Efficacy and Safety

• Studies have shown that phentermine is associated with clinically significant weight loss in adults, with some studies reporting an average weight loss of 5-10% of initial body weight 3, 7
• Phentermine is generally well-tolerated, with common side effects including dry mouth, insomnia, and constipation 3, 6
• Large-scale observational studies have not identified an increased risk of cardiovascular events or elevations in blood pressure associated with phentermine use 3
• However, there is limited evidence on the long-term efficacy and safety of phentermine, and more research is needed to fully understand its effects 3, 5