Phentermine may help certain patients lose more weight after discontinuing GLP-1s

Key takeaways:

• Patients on phentermine who gained weight on a GLP-1 had a median 3% weight loss the year after GLP-1 discontinuation.
• More research is needed on the long-term impacts of switching from GLP-1s to phentermine.

Patients who were prescribed phentermine after losing fewer than 20 pounds while on a GLP-1 receptor agonist were more likely to lose weight 1 year after GLP-1 discontinuation than those who were not prescribed phentermine, recent findings show.

The data are from a non-peer-reviewed report by Epic Research.

“Our findings suggest that primary care providers could consider prescribing phentermine to patients who have discontinued GLP-1 medications, especially if they lost less than 20 pounds while on the GLP-1 medication,” Kersten Bartelt, RN, a clinician at Epic Research, told Healio. “This could potentially help these patients maintain or even increase their weight loss.”

Previous research on weight regain after GLP-1 receptor agonist discontinuation is mixed. One trial showed that two-thirds of patients on once-weekly semaglutide 2.4 mg (Wegovy, Novo Nordisk) regained their weight 1 year after stopping the medication. Another report showed that more than half of patients who stopped semaglutide or liraglutide (Saxenda, Novo Nordisk) maintained their weight a year later.

In the current study, Bartelt and colleagues compared outcomes among 7,773 patients who were prescribed phentermine — approved by the FDA for weight management in 1959 — after discontinuing a GLP-1 receptor agonist with 34,668 patients who were not prescribed phentermine after GLP-1 discontinuation.

The researchers found that patients who gained or maintained weight while on a GLP-1 receptor agonist were more likely to lose weight after switching to phentermine, with a median weight loss of around 3% in the year after GLP-1 discontinuation.

In contrast, patients who switched to phentermine after losing at least 20 pounds while on a GLP-1 receptor agonist were more likely to regain weight 1 year after discontinuing the GLP-1 medication, with more than half regaining at least some of their weight.

Overall, patients who started phentermine after GLP-1 discontinuation were 29% less likely to regain all the weight they had lost 1 year later vs. patients who did not use phentermine after GLP-1 discontinuation (19.3% vs. 27.3%).

“While we found weight loss benefits for some patients who switched to phentermine, it is important to remember that individual patient characteristics, lifestyle choices, and personal circumstances are also factors and were not part of this study,” Bartelt said.

Future research, she added, could investigate the long-term impacts of switching from GLP-1 receptor agonists to phentermine.

“It would also be beneficial to investigate the factors that influence weight regain after discontinuing GLP-1 medications,” she said.

References:

• Patients who lose less than 20 pounds on GLP-1 treatment lose more weight after switching to phentermine. https://www.epicresearch.org/articles/patients-who-lose-less-than-20-pounds-on-glp-1-treatment-lose-more-weight-after-switching-to-phentermine. Published May 16, 2024. Accessed May 30, 2024.
• Many patients maintain weight loss a year after stopping semaglutide and liraglutide. https://epicresearch.org/articles/many-patients-maintain-weight-loss-a-year-after-stopping-semaglutide-and-liraglutide. Published Jan. 23, 2023. Accessed Jan. 31, 2023.
• Wilding J, et al. Diabetes Obes Metab. 2022;doi:10.1111/dom.14725.