From the Guidelines
Taking phentermine and GLP-1 receptor agonists together is not recommended without close medical supervision due to potential increased risk of side effects and interactions. The combination of these medications, which work through different mechanisms to promote weight loss, could lead to enhanced gastrointestinal side effects such as nausea, vomiting, and diarrhea 1. Phentermine, a stimulant that suppresses appetite by affecting the central nervous system, can increase heart rate and blood pressure, which might be problematic for some patients already using GLP-1 medications like liraglutide (Saxenda) or semaglutide (Wegovy, Ozempic) 1.
Key Considerations
- GLP-1 receptor agonists have a high glucose-lowering efficacy and promote weight loss by stimulating insulin secretion, reducing glucagon secretion, and improving satiety 1
- Phentermine is approved only for short-term use (3 months), but many providers prescribe it for longer durations as off-label therapy for continued weight management 1
- The combination of phentermine and GLP-1 receptor agonists may increase the risk of hypoglycemia, particularly when used with other medications that affect blood sugar levels 1
Recommendations
- If considering combination therapy, it is essential to have a thorough discussion with a healthcare provider to evaluate specific health status, weight loss goals, and potential risks
- The healthcare provider may recommend trying one medication first and assessing its effectiveness before considering combination therapy
- Close medical supervision is necessary to monitor for potential side effects and interactions when using phentermine and GLP-1 receptor agonists together 1
From the Research
Safety of Combining Phentermine and GLP-1 Receptor Agonists
The safety of taking phentermine and GLP-1 (Glucagon-like peptide-1) receptor agonists together is a topic of interest due to their potential synergistic effects on weight loss and metabolic parameters.
Metabolic and Cardiovascular Effects: A study published in 2019 2 investigated the effects of combining liraglutide (a GLP-1 receptor agonist) and phentermine in lean and obese male mice. The results showed that the combination produced the largest reduction in body weight in both groups, with modest improvements in cardiovascular functions in obese mice. However, in lean mice, the combination therapy did not improve cardiovascular parameters and even increased heart rate and reduced blood pressure.
Clinical Use and Indications: GLP-1 receptor agonists are approved for the treatment of type 2 diabetes and have been shown to have benefits in weight loss and blood pressure reduction 3, 4. Phentermine is an appetite suppressant used for short-term management of obesity. The combination of these drugs may be considered for patients with obesity and type 2 diabetes, but the potential for drug-drug interactions and adverse effects should be carefully evaluated.
Potential Drug-Drug Interactions: A retrospective analysis published in 2023 5 identified potential drug-drug interactions with phentermine among long-term phentermine consumers. The study found that co-prescription of phentermine with other drugs may result in moderate and severe interactions, highlighting the need for careful monitoring and management of patients taking phentermine and other medications, including GLP-1 receptor agonists.
Weight-Loss Therapy in Type 2 Diabetes: A study published in 2014 6 assessed the safety and efficacy of treatment with phentermine and topiramate extended release for weight loss and glycemic benefits in obese/overweight adults with type 2 diabetes. The results showed that the combination therapy plus lifestyle modification effectively promoted weight loss and improved glycemic control. However, this study did not specifically investigate the combination of phentermine and GLP-1 receptor agonists.
Key Considerations
When considering the combination of phentermine and GLP-1 receptor agonists, healthcare providers should carefully evaluate the potential benefits and risks, including the potential for drug-drug interactions and adverse effects. Patients should be closely monitored for changes in metabolic and cardiovascular parameters, as well as for any adverse events.