Evidence Library

GLP-1 medicines by the numbers: the key statistics, honestly sourced

By The Peptide Era editorial team·Independent medical review pending·Last reviewed July 2, 2026·11 sources

The short answer

These are trial averages from separate studies — not head-to-head, and not a prediction for any one person. Average weight loss ran about 21% for tirzepatide (Zepbound, SURMOUNT-1), about 16–17% for the oral-semaglutide pill (OASIS), about 15% for semaglutide (Wegovy, STEP 1), and about 11% for the orforglipron pill (Foundayo, ATTAIN-1); the investigational triple-agonist retatrutide reported about 28% at its top dose in a phase-3 readout that isn't yet published. The most common side effects are gastrointestinal (on the Wegovy label, nausea 44% vs 16% on placebo). Serious problems (gallbladder disease, pancreatitis) are uncommon; a rare eye condition (NAION) is an emerging, unproven signal. After stopping, trials show most of the lost weight returns over about a year. This page collects the key numbers, each tied to its source and labeled by how strong that evidence is.

Last reviewed July 2, 2026 against 11 sources below.

Key takeaways

01Average weight loss (each drug's own main trial): semaglutide ~15%, tirzepatide ~21%, orforglipron pill ~11%, oral semaglutide ~16–17%; investigational retatrutide ~28% at its top dose (topline, not yet published). Separate trials — not head-to-head, and an average is not a prediction for you.
02Side effects are mostly GI and mostly common-but-mild: on the Wegovy label, nausea 44% vs 16% on placebo, diarrhea 30% vs 16%, vomiting 24% vs 6%, constipation 24% vs 11%.
03Serious problems are uncommon: gallbladder/biliary disease is modestly increased (partly from rapid weight loss); the eye condition NAION is classed 'very rare' (≤1 in 10,000) and is an emerging, unproven signal.
04After stopping, the weight tends to come back: in the STEP 1 extension, participants regained about two-thirds of the lost weight within a year off the drug.

Safety essentials worth knowing

These apply to GLP-1 and dual/triple-agonist medicines generally. They’re label-level points, not the full list, and not advice about you — your prescriber and the FDA label are the authority.

Pregnancy & breastfeeding: these medicines are not recommended in pregnancy, and intentional weight loss is generally not advised in pregnancy; the labels advise stopping before a planned pregnancy. Breastfeeding status is a conversation to have with your clinician.
Birth control: some of these medicines (such as tirzepatide) can makeoral contraception less reliable. If you could become pregnant, ask about backup or non-oral contraception.
Thyroid boxed warning: this drug class carries an FDA boxed warning (thyroid C-cell tumours seen in rodents) and is not for people with a personal or family history of medullary thyroid cancer (MTC) or MEN 2.
Blood sugar: combined with insulin or a sulfonylurea, these medicines can cause low blood sugar — those other medicines often need prescriber-managed adjustment, not self-adjustment.
Eating disorders: an appetite-suppressing medicine warrants particular caution with a current or past eating disorder; disclose this to your clinician.
Surgery, sedation & endoscopy: because these medicines slow stomach emptying, tell your surgical or anaesthesia team you take a GLP-1 well in advance — they'll decide with you whether to continue or hold it (more).

Numbers are where the GLP-1 conversation gets slippery — a “20%!” here, a scary side-effect percentage there, usually with no source and no sense of how strong the evidence is. This page is the opposite: the figures people actually search for, each tied to its primary source and labeled by evidence type so you can weigh it. It’s education, not a prediction or medical advice. A running rule for the whole page: these are trial averages and population rates, not forecasts for any one person.

How much weight, on average

Each figure is that drug’s average in its own main obesity trial — separate studies, not a head-to-head, and individuals landed all over the average.

Medicine	Average weight loss	Trial	Evidence
Tirzepatide (Zepbound)	~20.9%	SURMOUNT-1, 72 wk (highest dose)	RCT (approved)
Oral semaglutide (oral Wegovy)	~16–17%	OASIS (adherent)	RCT (approved)
Semaglutide (Wegovy)	~14.9%	STEP 1, 68 wk	RCT (approved)
Orforglipron pill (Foundayo)	~11%	ATTAIN-1	RCT (approved)
Retatrutide (triple agonist)	~28% (top dose)	TRIUMPH-1, phase 3	Topline press release, not yet published — investigational (also ~30% in a higher-BMI subgroup)

The odds of hitting each milestone

From the two landmark trials — the share of participants who lost at least each amount (treatment-regimen estimand). This is what “individual results vary” looks like in numbers.

Lost at least…	Semaglutide (STEP 1)	Tirzepatide (SURMOUNT-1)
5%	~86%	~91%
10%	~69%	~84%
15%	~51%	~71%
20%	~32%	~57%

How common are the side effects

From the Wegovy (semaglutide) label, reported rates on the drug vs. on placebo. The gap over placebo is roughly the part attributable to the medicine — and a reminder that a chunk of every symptom happens on a sugar pill too.

Side effect	On the drug	On placebo
Nausea	44%	16%
Diarrhea	30%	16%
Vomiting	24%	6%
Constipation	24%	11%
Abdominal pain	20%	10%
Headache	14%	10%
Fatigue	11%	5%
Dyspepsia (indigestion)	9%	3%
Dizziness	8%	4%
GERD (reflux)	5%	3%

Most are mild-to-moderate, dose-related, and ease with time — see the side-effects page for the full picture.

Serious, but uncommon

Signal	The number	Evidence
Gallbladder / biliary disease	Modestly increased risk (relative risk ~1.4 in a 76-trial meta-analysis); small absolute risk, partly driven by rapid weight loss	Meta-analysis of RCTs
NAION (a rare eye condition)	Classed “very rare” — on the order of ≤1 in 10,000; cohort data suggest a roughly two-fold association	Emerging / observational — unproven, details
Pancreatitis, bowel obstruction (ileus)	Uncommon but labeled; the reason a few red-flag symptoms warrant prompt care	Labeled; ileus signal largely observational

What the numbers say about the benefits beyond weight

Finding	The number	Evidence
Cardiovascular risk (semaglutide, SELECT)	~20% relative reduction in major cardiovascular events (a smaller absolute difference — about 1.5 percentage points) in adults with obesity + established CVD	RCT (approved indication)
Lean (muscle) mass	In the STEP 1 body-composition sub-study, some of the weight lost was lean mass; the health significance is still being worked out	RCT sub-study — muscle page

After you stop

Finding	The number	Evidence
Weight regain	In the STEP 1 extension, participants regained about two-thirds of the lost weight within a year of stopping	RCT extension

The takeaway isn’t “don’t stop” — it’s that these medicines treat an ongoing condition, so stopping is a decision to plan with a clinician. See stopping a GLP-1 and the off-ramp planner.

Cost & coverage

Figure	The number	Evidence
Prior-auth appeals (Medicare Advantage, 2024)	Only ~11.5% of denied requests were appealed — but ~81% of those appeals were partially or fully overturned	KFF analysis

Most denials are never appealed, yet most appeals win — see cost & access for how to appeal.

Every figure above traces to the sources listed below. Where a number is from a topline press release (retatrutide) or observational data (NAION), it’s labeled as such — because a number is only as good as the evidence under it. For how we grade evidence, see the Evidence Ladder. And what any of these numbers mean for you is a conversation with a clinician who knows your history.

Sources (11)

Every claim on this page traces to a primary source — and we sell you nothing. No sponsors, no affiliate links, no ads.

5 randomized trials
2 news / agency
1 FDA labels
1 meta-analyses
1 other primary
1 reviews