Drug facts

Does compounded semaglutide work?

By David Chen·Editor·Reviewed September 2026

What semaglutide does¹

That was 1,961 adults without diabetes, double-blind, two-thirds of them on semaglutide and all with a lifestyle program. The thresholds show the spread behind the average: half the semaglutide group lost 15% or more, and half did not. The full summary is on STEP 1, and the head-to-head trials against tirzepatide are on semaglutide against tirzepatide.

Which semaglutide is in the vial⁴

With tirzepatide the open question is dose and quality. With semaglutide there is an earlier one: whether the vial contains the same active ingredient at all. FDA, in its own words:

The agency is aware that some semaglutide products sold by compounders may be the salt forms. These salt forms, including semaglutide sodium and semaglutide acetate, are different active ingredients than are used in the approved drugs. The agency does not have information on whether these salts have the same chemical and pharmacologic properties as the active ingredient in the approved drug, and we are not aware of any lawful basis for their use in compounding.

That is the one case on this page where “the molecule is the molecule” may not hold, and the evidence above may not describe what you are injecting. It is a question for the pharmacy, and a fair one to ask before a first order: what exactly is the active ingredient, and where does it come from? What else may be in a compounded vial is on what compounded semaglutide is.

Why it can seem not to work³

Some people lose little on semaglutide itself: in STEP 1, about one in seven of those weighed at week 68 had not lost 5%, and the weight curve flattened after week 60 — both are on not losing weight on semaglutide. The reasons below are timing, and the ones a compounded vial adds.

It is still early. Wegovy’s table calls weeks 1 to 4 the “Starting Dosage” and weeks 5 to 16 the “Dosage Escalation”; maintenance begins at week 17. In STEP 1 nobody started at 2.4 mg — the dose was climbed to. The dosage chart shows where you are on the ladder, and how long semaglutide takes to work covers what the trials saw in those weeks.

The dose is not the dose you think. This is the failure FDA has written about most specifically for semaglutide:⁴

FDA received multiple reports of adverse events, some requiring hospitalization, that may be related to dosing errors associated with compounded injectable semaglutide products. These dosing errors resulted from patients measuring and self-administering incorrect doses of the drug, and in some cases, health care professionals miscalculating doses of the drug.

A compounded vial’s concentration is set by the pharmacy, so the same milligram dose is a different mark on the syringe from vial to vial. If you have changed seller or vial, check the arithmetic before the next dose.

The vial is past its use. FDA says a vial holding several doses should be discarded 28 days after first use, and not used at all if it arrived warm — both covered in how long compounded semaglutide lasts.

What happens when it stops²

STEP 4 measured it by taking the drug away. 803 adults who had reached 2.4 mg and lost an average of 10.6% over a 20-week run-in were randomized to continue or switch to placebo. Over the following 48 weeks, those who continued lost a further 7.9%; those switched to placebo regained 6.9%. A result that fades after a gap in supply or a change of seller may be what stopping does, not the new vial failing. The trial is on STEP 4.

Where to take it

To the prescriber, with the vial’s label: the concentration, the dose you draw, the active ingredient if the pharmacy names it, and how long you have been on it. Whether to stay, step up or stop is a clinical decision. If price is what interrupts treatment, the cheapest semaglutide at every dose is what this site can help with.