From the Guidelines
Phentermine can be safe when used as prescribed by a healthcare provider for short-term weight loss, but it has significant risks and limitations, particularly in patients with a history of coronary artery disease, uncontrolled hypertension, glaucoma, and history of substance use disorder. According to a recent review published in JAMA in 2023 1, phentermine is the most commonly prescribed antiobesity medication and is an affordable alternative to other therapies. However, it has sympathomimetic effects, which can increase norepinephrine, leading to appetite suppression, but also potentially causing adverse cardiac events.
Key considerations for the safe use of phentermine include:
- Avoiding its use in patients with a history of coronary artery disease, uncontrolled hypertension, glaucoma, and history of substance use disorder
- Using it only for short-term weight loss (typically 12 weeks or less) in adults with a BMI of 30 or higher, or 27+ with weight-related conditions like hypertension or diabetes
- Monitoring for adverse effects, such as increased heart rate, elevated blood pressure, insomnia, dry mouth, constipation, and nervousness
- Classifying it as a controlled substance due to its potential for dependence and abuse
It is essential to note that phentermine should only be used alongside diet and exercise, not as a standalone solution, and requires medical supervision throughout treatment to monitor for adverse effects, as recommended by the study published in JAMA in 2023 1.
From the FDA Drug Label
WARNINGS AND PRECAUTIONS Coadministration with other drugs for weight loss is not recommended (safety and efficacy of combination not established). ( 5.1) Rare cases of primary pulmonary hypertension have been reported. Phentermine should be discontinued in case of new, unexplained symptoms of dyspnea, angina pectoris, syncope or lower extremity edema. ( 5. 2) Rare cases of serious regurgitant cardiac valvular disease have been reported. ( 5.3) The risks include, but are not limited to: Development of primary pulmonary hypertension [ see Warnings and Precautions ( 5. 2) ] Development of serious valvular heart disease [ see Warnings and Precautions ( 5.3) ]
Phentermine is not safe for everyone. The use of phentermine is associated with several serious risks, including:
- Primary pulmonary hypertension
- Serious valvular heart disease
- Increased blood pressure
- Risk of abuse and dependence Phentermine should be used with caution and under the guidance of a healthcare professional. Patients should be informed of the potential risks and monitored closely for any adverse reactions 2, 2, 2.
From the Research
Safety of Phentermine
- The safety of phentermine has been evaluated in several studies, with mixed results.
- A review of recent research on phentermine found that it is generally well tolerated, with no increased risk of cardiovascular events or elevations in blood pressure 3.
- However, a case report described a rare instance of phentermine-induced nonischemic cardiomyopathy in a 33-year-old female with no significant cardiac history 4.
- A study on the efficacy and safety of phentermine in adolescents found that it is an effective and safe means for weight loss in pediatric patients when combined with lifestyle interventions, with no severe adverse events reported 5.
- Another study found that phentermine/topiramate reduced body weight and blood pressure in people with elevated blood pressure, but also reported side effects such as dry mouth and paresthaesia 6.
Potential Side Effects
- Common side effects of phentermine include dry mouth, constipation, and headache 7, 6.
- More serious side effects, such as nonischemic cardiomyopathy, have been reported in rare cases 4.
- The long-term effects of phentermine on mortality and morbidity are not well established, and further research is needed to fully understand its safety profile 3, 6.
Special Considerations
- Phentermine is not recommended for long-term use, as its safety and efficacy for this duration are not well established 3.
- Patients with a history of cardiovascular disease or other health conditions should be closely monitored while taking phentermine 7, 6.
- Phentermine should be used in conjunction with lifestyle modifications, such as dietary changes and increased physical activity, for optimal weight loss and safety 5.