Bariatric surgery is the most durable weight-loss treatment there is, and a real proportion of people who have it do not get the result they hoped for. This is about what happens next, and it is the mirror image of taking the drug before the operation.
What was gathered
Studies of adults who had metabolic bariatric surgery at least a year before starting liraglutide, semaglutide or tirzepatide, reporting weight loss and adverse events. [1] Twenty-seven papers met the criteria and 19 went into the meta-analysis.
At twelve months, total body weight fell by 9.22% on liraglutide and by 9.02% on semaglutide. At six months, a comparison favored tirzepatide over semaglutide by a mean difference of 4.23% in total weight loss.
Why nine per cent is the right number to expect
It looks small against the fifteen per cent or more the obesity trials report, and the comparison is the wrong one. These are people who have already lost a great deal of weight surgically, so there is less left to lose. Their anatomy has been altered, which changes both absorption and satiety signaling. And they are, by selection, people whose response to a powerful intervention was already below average.
Nine per cent of body weight in that group is a substantial result. It is not the same result as nine per cent in somebody starting from scratch, and neither figure predicts the other — which is why a cost per kilogram computed from trial averages does not transfer to this situation.
The comparator is an operation
The authors frame these drugs as a possible alternative to revisional surgery — a second operation to revise or convert the first. That is the choice a patient in this position actually faces, and it is a genuine one: a second operation carries surgical risk, recovery time and cost, and a drug carries a monthly bill for as long as it is taken.
Nobody on this roster sells surgery of either kind and this site earns nothing from it, so the comparison can be stated without a thumb on the scale. Neither option is obviously right, and the durability question runs the other way from the price question — surgery is the more durable intervention and the drug is the one that stops working when you stop paying.
What the heterogeneity costs
The authors say their findings should be interpreted with caution given substantial heterogeneity across studies, and that caution applies hardest to the tirzepatide comparison. A 4.23% advantage at one timepoint, drawn from a varied literature, is a hypothesis about which drug to reach for, not an answer.
The durable point is simpler. If a first operation underdelivered, adding one of these drugs a year or more later produced meaningful further weight loss across most studies that looked — and, as everywhere else in this market, it produced it for as long as people kept taking it, at roughly a kilogram a month back once they stop.