From the Guidelines
Phentermine is a prescription medication used for short-term weight loss in obese individuals, typically prescribed at a dose of 15-37.5 mg once daily, and should be used in combination with diet and exercise for optimal results. The medication works by suppressing appetite through the activation of the sympathetic nervous system, leading to a decrease in food intake and an increase in resting energy expenditure 1. According to 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, with 46% of subjects achieving 5% weight loss and 20.8% achieving 10% weight loss 1.
Key Considerations
- The recommended dosage of phentermine is 15 to 37.5 mg orally once daily in the morning, with a low-dose option of 8-mg tablets 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, particularly younger patients without evidence of active or unstable coronary disease, or uncontrolled hypertension 1.
Patient Selection and Monitoring
- Patients who have anxiety or insomnia might feel their condition is exacerbated by phentermine, and would not be ideal candidates 1.
- Phentermine requires close medical supervision and should not be used as a long-term solution for weight management, due to the potential for dependence and the lack of long-term safety trials 1.
From the FDA Drug Label
Phentermine Hydrochloride is a sympathomimetic amine anorectic 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).
The use of Phentermine (Adipex-P) is as a short-term adjunct in a weight reduction regimen for patients with:
- An initial body mass index (BMI) greater than or equal to 30 kg/m^2
- Or a BMI greater than or equal to 27 kg/m^2 with other risk factors such as:
- Controlled hypertension
- Diabetes
- Hyperlipidemia This is based on a regimen of exercise, behavioral modification, and caloric restriction 2.
From the Research
Use of Phentermine (Adipex-P)
- Phentermine is a sympathomimetic amine approved for the short-term treatment of patients with obesity 3, 4, 5, 6.
- It is used in conjunction with lifestyle modifications, such as diet and exercise, to treat obesity 3, 7, 5, 6.
- Phentermine is indicated for short-term use, as long-term use may be associated with severe cardiovascular side effects, abuse, and dependence 4.
- The drug has appetite-suppressing properties and is used to promote weight loss 4, 5, 6.
Clinical Use and Considerations
- Phentermine is contraindicated in patients with cardiovascular disease or uncontrolled hypertension 3.
- Clinicians should be cautious when prescribing phentermine due to the potential for drug-drug interactions and adverse drug reactions 4.
- Atrial fibrillation is a rare but potential cardiovascular side effect of phentermine 7.
- The importance of medication reconciliation is essential to rule out secondary causes of adverse effects, including medication side effects 7.
Combination Therapy
- Phentermine has been used in combination with topiramate for the management of obesity, with clinical trial data supporting effective and sustained weight loss 5, 6.
- The fixed-dose combination of phentermine and extended-release topiramate (Qsymia) is approved by the FDA for the treatment of obesity 5.
- This combination therapy has been shown to promote weight reduction and improve adverse metabolic consequences in obesity 6.