Taking a GLP-1 medication before bariatric surgery did not appear to give patients an extra weight-loss advantage during the first year after surgery, according to a new study.
Researchers followed 383 patients who underwent bariatric surgery at one medical center between 2022 and 2024. About one-quarter were taking a GLP-1 medication before surgery, most commonly semaglutide. One year later, patients who had used a GLP-1 drug before surgery had lost an average of 24% of their total body weight, compared with 25% among those who had not used one.
The difference was not statistically significant.
The study, published in JAMA Surgery, adds to a growing question in obesity care as more people taking medications such as semaglutide or tirzepatide later go on to have bariatric surgery: Does using the drugs first improve the amount of weight people lose after surgery?
In this study, the answer was no, at least during the first 12 months.
Researchers reviewed medical records for patients who underwent either sleeve gastrectomy or gastric bypass. Ninety-two were taking a GLP-1 medication before surgery.
The two groups were similar in age, body mass index and sex, although there were some important differences. Type 2 diabetes was much more common among patients taking GLP-1 medications, affecting 51% of that group compared with 16% of patients who were not taking the drugs.
Researchers accounted for several of those differences in their statistical analysis, including age, body mass index, sex, race and ethnicity, diabetes, smoking status and type of surgery. Preoperative GLP-1 use still was not associated with greater weight loss after 12 months.
There also were no significant differences between the groups in hospital stay, operating time, emergency department visits within 30 days or complications.
Blood sugar control was similar as well. Average hemoglobin A1c levels were about 5.4% among patients who had used GLP-1 medications and 5.3% among those who had not.
The findings do not mean GLP-1 medications have no role before bariatric surgery.
People may take the drugs before surgery for reasons other than trying to increase their eventual surgical weight loss, including treatment of type 2 diabetes or weight management before a procedure. The study also did not measure how much weight patients had already lost from GLP-1 medications before surgery.
That is an important limitation because someone who loses weight on a medication before surgery could ultimately reach a similar weight as someone who begins surgery at a higher starting point, even if their postoperative weight-loss percentages look alike.
Researchers also could not reliably determine how long patients had been taking GLP-1 medications before surgery. Most had not reached the maximum dose, and only four of the 92 patients in the GLP-1 group were taking tirzepatide.
Most patients stopped the medication after surgery on their medical team’s recommendation to reduce the risk of vomiting. Fifteen restarted a GLP-1 medication during the following year, including five for diabetes management and eight for weight control.
The study was also conducted at a single center and was not randomized. Patients who were prescribed GLP-1 medications differed from those who were not, particularly in their rate of type 2 diabetes, so the findings cannot prove that using or not using the drugs before surgery directly caused the similar weight-loss outcomes.
The researchers noted that other recent studies have reached broadly similar conclusions, finding no clear improvement in one-year surgical weight loss among patients who used GLP-1 medications beforehand.
Another study, however, found that patients taking semaglutide lost some weight before surgery and then lost less afterward, leaving their total weight loss at 12 months roughly similar to people who had surgery without prior GLP-1 treatment.
Taken together, the emerging research suggests that GLP-1 medications do not simply add another layer of weight loss on top of bariatric surgery.
But researchers still do not know the best way to sequence the two treatments, how longer-term outcomes compare or whether particular groups of patients could benefit from using both at different stages of treatment.
For now, the new study suggests that arriving at bariatric surgery while already taking a GLP-1 medication does not necessarily translate into greater weight loss during the following year.
The published research letter does not report study funding or grant support. The authors reported no conflicts of interest. The research was presented at the Pacific Coast Surgical Association Meeting in February 2026.