From the Guidelines
Phentermine is typically prescribed for patients with a BMI of 30 kg/m² or higher, or for those with a BMI of 27 kg/m² or higher who also have at least one weight-related condition, as recommended by the most recent guidelines 1. The medication is intended for short-term use (usually up to 12 weeks) as part of a comprehensive weight management program that includes dietary changes and increased physical activity. Key points to consider when prescribing phentermine include:
- The recommended dosage of phentermine is 15 to 37.5 mg orally once daily in the morning 1
- Phentermine is a controlled substance due to its stimulant properties and potential for abuse
- Before starting phentermine, patients should undergo a thorough medical evaluation to ensure they don't have contraindications such as heart disease, uncontrolled hypertension, hyperthyroidism, glaucoma, history of drug abuse, or pregnancy
- Regular monitoring during treatment is essential to assess effectiveness and watch for side effects like increased blood pressure, insomnia, dry mouth, and constipation
- According to the most recent study, phentermine alone (15 mg daily) was associated with a 6.0-kg weight loss at 28 weeks, compared with a placebo 1
- The most 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
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 BMI criteria for phentermine use are:
- Greater than or equal to 30 kg/m 2
- Greater than or equal to 27 kg/m 2 in the presence of other risk factors, such as:
From the Research
Phentermine BMI Criteria
- The BMI criteria for phentermine use is typically for individuals with a body mass index (BMI) of 27-45 kg/m(2) and two or more comorbidities, such as hypertension, dyslipidaemia, diabetes or prediabetes, or abdominal obesity 3.
- Studies have shown that phentermine/topiramate therapy can be effective for weight loss in adults with overweight or obesity, with an average weight loss of 7.73 kg (95% CI: 6.60-8.85) compared to placebo 4.
- The efficacy of phentermine/topiramate therapy is closely related to the dosage, with higher doses resulting in greater weight loss 4.
- Phentermine/topiramate extended release (ER) has been shown to be effective in promoting weight loss and improving glycemic control in obese/overweight patients with type 2 diabetes, with a mean baseline BMI of 27-45 kg/m(2) 5.
- Changes in cardiovascular risk factors, such as lipid variables and blood pressure, have been observed in obese patients with dyslipidemia and/or hypertension receiving phentermine and topiramate extended-release, with a BMI of 27 to 45 kg/m(2) 6.
- Longer-term use of phentermine has been associated with greater weight loss without increased risk of incident cardiovascular disease or death, in patients with a mean baseline BMI of 37.8 (7.2) kg/m2 7.