Both, and they answer different problems. Taking one in the year before an operation went with fewer early complications. Within 90 days, 0.3% of prior users had a cardiovascular event against 0.6% of matched non-users [1]. Taking one afterwards is about weight the operation did not remove. The pooled figure there is roughly 9% further weight loss at a year [3].
Almost everything written about these drugs and surgery treats them as alternatives. The literature increasingly treats them as a sequence. That matters, because surgery is the most durable option in the real-world evidence, and nobody here sells it.
Before: what was compared
Adults who had metabolic and bariatric surgery between 2016 and 2025 in a US records database. Prior use meant at least one GLP-1 or tirzepatide prescription between 365 and 7 days before the operation. Anybody with a prescription closer than that was excluded. Prior users and non-users were matched one to one, leaving 11,052 in each group. Follow-up ran from the first postoperative day through day 90.
That seven-day exclusion is a design choice worth naming. It removes the separate question of whether these drugs complicate anesthesia, covered in the fasting and endoscopy evidence. What is left is a cleaner question about sequencing.
Before: what was found, both ways round
Four-point major adverse cardiovascular events occurred in 36 prior users and 67 non-users. That is 0.3% against 0.6%, hazard ratio 0.535, 95% CI 0.357 to 0.803. Early postoperative kidney events occurred in 158 and 256. That is 1.4% against 2.3%, hazard ratio 0.613, 95% CI 0.502 to 0.747. Coronary events and heart failure also came in lower.
Who takes a GLP-1 before bariatric surgery
Not a random sample of surgical candidates. Getting a prescription filled in the year before an elective operation requires a prescriber, usually insurance, and sustained engagement with care.
Propensity matching balances what the records contain. It cannot balance conscientiousness, social support, or the quality of the practice somebody attends. That this drug reaches better-insured and higher-income patients is itself measured in income and private coverage predict who gets it. Those same characteristics predict recovering well. The effect size is modest enough to be believable. The structure is still observational.
After: starting one before anything goes wrong
A prospective study added semaglutide about five months after sleeve gastrectomy in patients with class II or III obesity [2]. At a year they were 4.4 percentage points further down than the comparison group.
Nobody was randomized, and that matters here more than usual. An early adjuvant goes to the patients whose surgeons thought they needed one. That pushes the estimate in a direction nobody can size, and the study design is the finding.
After: when the operation underdelivered
The larger evidence base covers rescue rather than prevention. It pools studies of people whose bariatric surgery fell short, or whose weight returned. These drugs produced about 9% further weight loss at a year.
The alternative there is a second operation. That is the comparison worth pricing, and what rescue therapy replaces sets it out alongside the break-even arithmetic.
What none of it covers
The before study runs 90 days. Nothing about weight a year later. Nothing about whether the surgery worked better. Nothing about whether a drug first meant surgery at all. The authors call their finding support for further investigation of preoperative metabolic optimization, which is the appropriately narrow conclusion.
If surgery is on your list of options, ask a surgical team about sequencing. The two are not rival purchases. Nobody on this roster sells surgery, earns anything from it, or can advise on it. What this site can tell you is what the drug half costs while you decide, in the six-month view.