Metformin vs Semaglutide: side effects in FDA adverse event reports
At a glance
| Metformin | Semaglutide | |
|---|---|---|
| Drug class | – | GLP-1 Receptor Agonist |
| Brand names | Metformin Hydrochloride | Wegovy |
| FAERS reports | 354,745 | 72,971 |
| Serious | 69% | 50% |
| Death outcome | 29,950 | 1,270 |
| Boxed warning | Yes LACTIC ACIDOSIS Postmarketing cases of metformin-associated lactic acidosis have resulted in death, hypothermia, hypotension, and resistant bradyarrhythmias. Th | Yes RISK OF THYROID C-CELL TUMORS • In rodents, semaglutide causes dose-dependent and treatment-duration-dependent thyroid C-cell tumors at clinically relevant expo |
Signals both drugs share
| Reaction | Metformin | Semaglutide | Label screen (A / B) |
|---|---|---|---|
| Euglycaemic diabetic ketoacidosis | 1,754 · PRR 46.1 | 186 · PRR 14.0 | Labeled (related wording) / Not in label — unassessed |
| Diabetic retinopathy | 389 · PRR 7.5 | 160 · PRR 14.1 | Likely indication confounding / Labeled — boxed warning |
| Impaired gastric emptying | 1,751 · PRR 9.3 | 3,558 · PRR 111.3 | Not in label — unassessed / Not in label — unassessed |
| Gastrointestinal hypomotility | 384 · PRR 12.1 | 489 · PRR 80.6 | Not in label — unassessed / Not in label — unassessed |
Labeled signals distinctive to Metformin
- Acute kidney injury — n=17,231, PRR 7.4 Labeled — boxed warning
- Lactic acidosis — n=17,141, PRR 67.6 Labeled — boxed warning
- Hypoglycaemia — n=7,287, PRR 10.3 Labeled — boxed warning
- Metabolic acidosis — n=6,200, PRR 14.2 Labeled adverse reaction
- Diabetic ketoacidosis — n=4,053, PRR 11.9 Labeled adverse reaction
- Diabetes mellitus inadequate control — n=2,895, PRR 11.4 Labeled (related wording)
- Ketoacidosis — n=1,347, PRR 12.8 Labeled adverse reaction
- Vitamin b12 deficiency — n=630, PRR 10.8 Labeled (related wording)
Labeled signals distinctive to Semaglutide
- Eructation — n=1,059, PRR 16.9 Labeled adverse reaction
- Ileus — n=632, PRR 15.5 Labeled adverse reaction
- Injection site discharge — n=213, PRR 12.5 Labeled (related wording)
- Gallbladder injury — n=139, PRR 22.1 Labeled (related wording)
- Allodynia — n=83, PRR 22.8 Labeled adverse reaction
- Medullary thyroid cancer — n=61, PRR 63.6 Labeled (related wording)
Common questions
Which has more reported side effects, Metformin or Semaglutide?
Metformin has 354,745 FAERS reports and Semaglutide 72,971. More reports does not mean more dangerous: volume follows how widely and how long a drug has been used, prescription vs over-the-counter status, and publicity. The seriousness share (69% vs 50%) is a better like-for-like signal of the kind of problems reported.
Which side effects do Metformin and Semaglutide share?
Both drugs carry disproportionality signals for euglycaemic diabetic ketoacidosis, diabetic retinopathy, impaired gastric emptying, gastrointestinal hypomotility. Shared signals often reflect a shared drug class or the condition both are used for.
Is Metformin or Semaglutide safer?
FAERS cannot answer that: it has no denominator and no comparator. Use this page to see which risks are already on each label and which signals are unlabeled, then check the prescribing information and your clinician for your situation.
Sources: openFDA FAERS pair statistics (OpenPV build 2026-09-14), FDA labels via openFDA, openFDA count queries for seriousness and deaths. Pair chosen because it is a commonly searched comparison. Generated 2026-10-08.