What are the guidelines for using Adipex (phentermine) for weight loss?

From the Guidelines

Adipex (phentermine) should only be used for weight loss under a doctor's prescription as part of a comprehensive program that includes diet and exercise for adults with a BMI of 30 or higher, or 27+ with weight-related conditions, with a recommended dosage of 15-37.5 mg orally once daily in the morning, and treatment generally limited to 12 weeks maximum due to diminishing effectiveness and risk of dependence, as suggested by the most recent guideline from the American Gastroenterological Association (AGA) in 2022 1.

Key Considerations for Phentermine Use

• The typical dosage is 15-37.5 mg taken once daily in the morning before breakfast, though some patients may start with a lower dose.
• Phentermine works by suppressing appetite through stimulating the central nervous system and increasing norepinephrine levels in the brain.
• Common side effects include dry mouth, insomnia, constipation, and increased heart rate.
• It should be avoided by people with heart disease, uncontrolled hypertension, hyperthyroidism, glaucoma, history of drug abuse, or during pregnancy.
• Patients should avoid taking it late in the day to prevent sleep disturbances and should not combine it with other stimulants or weight loss medications unless specifically directed by their doctor.
• Regular monitoring of blood pressure and heart rate is necessary throughout treatment, as recommended by the AGA guideline 1.

Patient Selection and Monitoring

• Appropriate candidates for phentermine include patients with obesity who need assistance with appetite suppression, as stated in a study published in Gastroenterology in 2017 1.
• Patients who have anxiety or insomnia might feel their condition is exacerbated by phentermine, and would not be ideal candidates.
• The AGA guideline suggests using phentermine with lifestyle modifications, compared with lifestyle modifications alone, for adults with obesity or overweight with weight-related complications, with a conditional recommendation and low-quality evidence 1.

Safety and Efficacy

• Phentermine is a Schedule IV medication, and its use should be carefully monitored due to the risk of dependence.
• The efficacy of phentermine for weight loss has been demonstrated in several studies, including a 28-week, randomized, controlled trial comparing phentermine/topiramate extended-release with phentermine monotherapy and topiramate monotherapy in adults with obesity, which showed that phentermine alone was associated with a 6.0-kg weight loss at 28 weeks, compared with a placebo 1.
• The AGA guideline suggests that phentermine monotherapy is approved by the FDA for short-term use (12 weeks), but many practitioners use phentermine longer than 12 weeks in an off-label fashion, and phentermine should be avoided in patients with a history of cardiovascular disease, with blood pressure and heart rate monitored periodically while taking phentermine 1.

From the FDA Drug Label

Phentermine Hydrochloride, USP 15 mg and 30 mg is indicated as a short-term (a few weeks) adjunct 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).

The guidelines for using Adipex (phentermine) for weight loss are:

• Short-term use: Phentermine is indicated for short-term use (a few weeks) as an adjunct to a weight reduction regimen.
• BMI requirements: Patients should have an initial body mass index (BMI) greater than or equal to 30 kg/m2, or greater than or equal to 27 kg/m2 with other risk factors (e.g., controlled hypertension, diabetes, hyperlipidemia).
• Regimen components: The weight reduction regimen should include exercise, behavioral modification, and caloric restriction.
• Patient counseling: Patients must be informed about the risks and benefits of phentermine, including the potential for developing tolerance, dependence, and interactions with other drugs 2, 2.

From the Research

Guidelines for Using Adipex (Phentermine) for Weight Loss

• Adipex, also known as phentermine, is a weight-loss medication that should be used as part of a comprehensive program of diet, exercise, and behavior therapy 3.
• The medication is typically prescribed for short-term use, but recent studies have shown that it can be effective for long-term weight loss when used in combination with lifestyle modification 4, 5.
• Phentermine works by manipulating the control of hunger and satiety in the central nervous system, and it has been shown to promote modest weight loss when given along with recommendations for diet 6.
• The amount of weight loss seen with phentermine varies, but it generally falls in the range of 3-10% of starting weight, and it requires continual use of the drug to be sustained 4, 7.
• Phentermine is one of seven FDA-approved anti-obesity medications, and it should be prescribed with the intention of long-term use as part of a multidisciplinary approach to obesity management 5.

Important Considerations

• Phentermine should be used in combination with lifestyle modification, including dietary changes and increased physical activity, to achieve optimal weight loss results 3, 5.
• The medication has a unique side effect profile that should be carefully considered when selecting the best agent for a given individual 4, 7.
• High attrition rates have been associated with lower confidence in estimates of weight loss and adverse events, highlighting the importance of close monitoring and support for patients using phentermine for weight loss 7.
• Phentermine-topiramate, a combination medication that includes phentermine, has been shown to be associated with the highest odds of achieving at least 5% weight loss at 52 weeks, but it also has a higher risk of adverse event-related treatment discontinuation 7.