Reviewed by Ashley Harwyn, PA-C  |  A4M Board Certified  |  Updated September 4, 2026

Weight loss medication is the most talked-about thing in medicine right now and one of the worst-described. This page gives you the actual trial numbers, the actual side effect rates, and the FDA's actual position on the cheaper compounded versions, so the decision is yours rather than an advertisement's.

What do these medications actually do?

STEP 1 enrolled 1,961 adults with a BMI of 30 or greater, or 27 with a weight-related condition, and no diabetes. Over 68 weeks the semaglutide group lost a mean 14.9 percent of body weight against 2.4 percent on placebo, an estimated treatment difference of 12.4 percentage points[1]. In kilograms that was 15.3 against 2.6.

SURMOUNT-1 enrolled 2,539 adults on the same criteria and ran 72 weeks. At 15 mg, tirzepatide produced a mean 20.9 percent reduction against 3.1 percent on placebo[2]. At 5 mg it was 15.0 percent and at 10 mg 19.5 percent, so the dose matters and the trial says by how much.

Both trials ran the medication alongside lifestyle intervention, not instead of it. That is the part that gets dropped in the retelling, and it is the reason a prescription on its own is not the program. It is also why the assessment here starts with a lab panel and a body composition baseline rather than with a dose.

How many people actually responded

Averages hide the spread, so here is the distribution. In STEP 1, 86.4 percent of the semaglutide group lost at least 5 percent of body weight, 69.1 percent lost at least 10 percent, and 50.5 percent lost at least 15 percent, against 31.5, 12.0 and 4.9 percent on placebo[1].

In SURMOUNT-1 at 15 mg, 91 percent lost at least 5 percent and 57 percent lost at least 20 percent, against 35 percent and 3 percent on placebo[2]. Those are strong results by any standard in this field. They are also not universal, and a plan that assumes you will land at the top of that range is a plan with no fallback.

What are the side effects, honestly?

Mostly gastrointestinal, mostly early, and mostly not trivial to live through. In STEP 1 the most common adverse events on semaglutide were nausea and diarrhea, typically transient and mild to moderate, subsiding with time. Even so, 4.5 percent of the semaglutide group discontinued treatment because of gastrointestinal events against 0.8 percent on placebo[1].

SURMOUNT-1 reported the same pattern, with most events mild to moderate and occurring mainly during the 20-week dose escalation. Adverse events caused discontinuation in 4.3 percent at 5 mg, 7.1 percent at 10 mg and 6.2 percent at 15 mg, against 2.6 percent on placebo[2].

Is compounded semaglutide the same thing?

No, and this is the part of the market where the price difference comes from. The FDA states plainly that it does not review compounded drugs for safety, effectiveness or quality before they are marketed[3]. A compounded preparation is not the product that was studied in the trials above.

The agency has also raised a specific chemical concern. Salt forms including semaglutide sodium and semaglutide acetate are different active ingredients from the ones in the approved drugs, and the FDA says it is not aware of any lawful basis for their use in compounding[3].

The reporting bears this out. As of May 31, 2026 the FDA had received 990 reports of adverse events associated with compounded semaglutide and more than 730 associated with compounded tirzepatide, along with multiple reports of adverse events, some requiring hospitalization, that may relate to dosing errors with compounded injectable semaglutide[3]. Its guidance for anyone buying online is to purchase only from state-licensed pharmacies.

The question to ask any clinic, including this one

Ask which specific product you are being prescribed, whether it is the FDA-approved medication or a compounded preparation, and which pharmacy dispenses it. It is a fair question, it has a one-sentence answer, and how readily it is answered tells you most of what you need to know about where you are. Then ask what the monitoring schedule is and what happens if you stop.

Why the assessment comes before the prescription

Medication is one tool and it is not required. What does not change is the assessment, because several of the common reasons weight will not move are measurable and treatable on their own: thyroid function, blood sugar handling, sleep quality, iron status, and the effects of medications already being taken.

Screening for prediabetes and type 2 diabetes carries a formal recommendation for adults aged 35 to 70 with overweight or obesity, and it is inexpensive. If one of those items is the cause, finding it changes the plan entirely, and finding it after a year of treatment aimed somewhere else is a poor trade. See full panel lab testing and thyroid management.