There are no official guidelines to assist in answering this question. I will search for relevant research papers instead.
From the FDA Drug Label
- 1 Coadministration with Other Drug Products for Weight Loss
Phentermine is indicated only as short-term (a few weeks) monotherapy for the management of exogenous obesity The safety and efficacy of combination therapy with phentermine and any other drug products for weight loss including prescribed drugs, over-the-counter preparations, and herbal products, or serotonergic agents such as selective serotonin reuptake inhibitors (e.g., fluoxetine, sertraline, fluvoxamine, paroxetine), have not been established. Therefore, coadministration of phentermine and these drug products is not recommended.
The use of phentermine with fluoxetine (Prozac) is not recommended due to the lack of established safety and efficacy of combination therapy with phentermine and serotonergic agents, including selective serotonin reuptake inhibitors (SSRIs) like fluoxetine 1.
From the Research
Safety of Combining Phentermine and Fluoxetine
The safety of taking phentermine and fluoxetine (Prozac) together is a concern due to potential drug-drug interactions.
- A study from 2007 2 compared the combination of phentermine and fluoxetine to phentermine and fenfluramine for obesity treatment, finding that the phentermine-fluoxetine combination was not as effective but did not cause cardiac valve lesions.
- Another study from 2000 3 found that fluoxetine increased the anorectic and dopamine-depleting effects of phentermine in mice, suggesting potential increased toxicity.
- However, there is limited research directly addressing the safety of combining phentermine and fluoxetine in humans.
Potential Interactions and Side Effects
- The combination of phentermine and fluoxetine may increase the risk of adverse drug reactions due to potential drug-drug interactions 4.
- Fluoxetine may potentiate the effects of phentermine, leading to increased anorectic and dopamine-depleting effects 3.
- The long-term use of phentermine may be associated with severe cardiovascular side effects, abuse, and dependence 4.
Clinical Considerations
- A study from 2005 5 reviewed the effect of pharmacologic agents, including phentermine and fluoxetine, on long-term weight loss, finding that extended treatment may be beneficial for some patients.
- However, the clinical significance of combining phentermine and fluoxetine remains to be ascertained, and further research is needed to fully understand the potential risks and benefits 3.