# Which GLP-1 Has the Worst Side Effects? It Depends on the Outcome | This GLP A meta-analysis of ten studies found tirzepatide produced 4.28 points more weight loss than semaglutide — and a higher rate of serious adverse events. Publisher: This GLP Editorial Team Canonical: https://thisglp.com/research/which-glp1-has-the-worst-side-effects Updated: 2026-10-26 Published: 2026-09-16 [← Research](https://thisglp.com/research) Evidence # Which GLP-1 Has the Worst Side Effects? It Depends on the Outcome Pooling 41,381 people, the two drugs looked alike on ordinary side effects and on quitting. Serious adverse events were 83% more frequent with tirzepatide. [This GLP Editorial Team](https://thisglp.com/about)September 20266 min read Tirzepatide against semaglutide, by event category · overall adverse events · similar · gastrointestinal events · similar · stopped for adverse events · RR 1.28, p = 0.54 · serious adverse events · RR 1.83, p = 0.007 · Ten studies, 41,381 participants — and no interval published for the one that moved **Research, not medical advice.** This GLP is independent and educational. Nothing here is a substitute for individualized care from a licensed clinician, and reading it creates no doctor–patient relationship. Talk to your own provider before starting, stopping, or changing any medication, peptide, or therapy. See our [methodology](https://thisglp.com/methodology) and [terms](https://thisglp.com/terms). ## Key takeaways - A meta-analysis pooled ten studies and 41,381 participants comparing tirzepatide with semaglutide over at least 24 weeks. - Tirzepatide produced 4.28 percentage points more weight loss, 95% CI −5.28 to −3.28, and 4.43 kg more in absolute terms. - It was likelier to reach 10%, 15% and 20% weight loss. At 5% there was no difference — both drugs get most people there. - Overall adverse events, gastrointestinal events and discontinuation for side effects were all similar. - Serious adverse events were more frequent with tirzepatide: risk ratio 1.83, p=0.007, with no interval published in the abstract. On serious events, they stop looking alike, and the answer depends on which outcome you pick. The pooled analysis below is where the two drugs separate. For claims encountered outside a study, see the [analysis of GLP-1 advice on social media](https://thisglp.com/research/can-you-trust-glp1-advice-on-social-media). It asks whether popularity is a useful signal of information quality. Direction can also flip with the comparator. In veterans with type 2 diabetes and opioid use disorder, overdose risk fell against two comparator drugs and not against three [\[2\]](https://thisglp.com/research/which-glp1-has-the-worst-side-effects#ref-2). So [the answer changed with what the drug was set beside](https://thisglp.com/research/overdose-depends-on-the-comparator). That is true of most claims in this class. This site already covers the largest single cohort comparing these two drugs. It found tirzepatide ahead on weight and [most of each group gone before the end](https://thisglp.com/research/tirzepatide-vs-semaglutide-which-works-better). This is the pooled version, and it adds one finding the cohort did not report. ## The efficacy side, briefly Ten studies, randomized and observational, with at least 24 weeks of follow-up, covering 41,381 participants. [\[1\]](https://thisglp.com/research/which-glp1-has-the-worst-side-effects#ref-1) Tirzepatide produced 4.28 percentage points more weight reduction, 95% CI −5.28 to −3.28. Absolute loss ran 4.43 kg greater, 95% CI −5.56 to −3.30. Glycated hemoglobin fell 0.29 percentage points further. It was likelier to get people past 10%, 15% and 20% weight loss. At the 5% threshold there was no difference. Both drugs get most people that far. The separation is entirely in the deeper end. Pooling randomized trials with observational studies invites an obvious objection. The authors addressed it. Subgroup analyses by study design produced consistent findings, as did subgroups by diabetes status. ## The finding that is new here Three safety comparisons came back level. Overall adverse events were similar. Gastrointestinal adverse events were similar. Discontinuation because of adverse events was similar, at a risk ratio of 1.28 with p=0.54. Serious adverse events were not. They were more frequent with tirzepatide, risk ratio 1.83, p=0.007. What that category means, and what the abstract omits A serious adverse event is a regulatory classification. Death, hospitalization, significant disability, a life-threatening episode. Recorded whether or not anybody thinks the drug caused it. So this is not 83% more harm; it is 83% more events in a bucket defined by severity rather than by attribution. The abstract publishes no confidence interval for that risk ratio, only the point estimate and the p-value. The finding cannot be sized. It is a real signal that cannot be measured from what was reported. ## Why the pattern is the interesting part If tirzepatide were simply harder to tolerate, it should show up in the ordinary adverse events and in people quitting. It did not. The two drugs looked alike on everything except the most severe category. That could mean several things. It could reflect the greater metabolic effect of the stronger drug producing more events at the tail. It could be a consequence of who receives which drug in the observational studies. It could be a chance finding in a category with few events. That is exactly why the missing interval matters, and why [a signal without its uncertainty](https://thisglp.com/research/do-glp1-drugs-cause-arrhythmia) is so hard to use. ## What a reader should take from it The efficacy gap is well established and this adds to it. Tirzepatide takes off more weight, and the advantage is concentrated among people aiming past ten percent rather than at modest loss. The safety gap is a question rather than an answer, and it is one nobody selling either drug will raise. A seller comparing the two has every reason to quote the weight difference and none to mention a serious adverse event ratio. and [almost nothing about safety appears there at all](https://thisglp.com/tools/what-sellers-publish). Where the two drugs genuinely look alike, that is worth knowing too, because [similar is not the same as identical](https://thisglp.com/research/does-a-glp1-affect-surgery-outcomes). Unlike most comparisons in this field, these studies put the two drugs against each other directly. ## Frequently asked How much more weight does tirzepatide take off? 4.28 percentage points more than semaglutide, 95% CI −5.28 to −3.28, or 4.43 kg in absolute terms across ten studies. What does a higher serious adverse event rate mean? A serious adverse event is a regulatory category — death, hospitalization, significant disability, a life-threatening episode — logged whether or not the drug is thought to have caused it. The risk ratio was 1.83 with p=0.007, and the abstract publishes no confidence interval for it. Were ordinary side effects worse? No. Overall adverse events, gastrointestinal events and discontinuation because of side effects were all similar between the two drugs. Does the weight advantage apply to everyone? Not evenly. There was no difference at the 5% weight-loss threshold, and the advantage appeared at 10%, 15% and 20%. ## Sources 1. \[1\] Paccola GP, et al. (2026). Comparative Efficacy of Tirzepatide Versus Semaglutide for Weight Loss in Adults With Overweight or Obesity: A Systematic Review and Meta-Analysis of Head-to-Head Studies Clinical Obesity. [PMID 42670242](https://pubmed.ncbi.nlm.nih.gov/42670242/) 2. \[2\] Kennedy KP, Bremseth-Vining R, Lynch KG, Reville N, et al. (2026). GLP-1 Receptor Agonists and All-Cause Overdose Risk in Veterans With Type 2 Diabetes and Opioid Use Disorder The Journal of Clinical Psychiatry. [PMID 42474323](https://pubmed.ncbi.nlm.nih.gov/42474323/) ## More in Evidence - [ 150 minutes · Weekly activity goal · 2 days · Muscle strengthening · Adapt · Symptoms and ability ### Exercise on Ozempic: Building Strength Without Ignoring Symptoms ](https://thisglp.com/research/exercise-on-ozempic) - [ STEP 1, semaglutide 2.4 mg vs placebo, % change at 68 weeks · LDL cholesterol · −2.5% vs +1.3% · Total cholesterol · −3.3% vs +0.1% · HDL cholesterol · +5.2% vs +1.4% · Triglycerides · −21.9% vs −7.3% · Wegovy label, Table 13. Adults without diabetes. Ozempic doses are lower. ### Does Ozempic Lower Cholesterol? What the Lipid Results in the Trials Show ](https://thisglp.com/research/does-ozempic-lower-cholesterol) - [ Where the insulin reduction came from, units per day · week 4 · 13.4 total · week 26 · 21.9 · the drug itself · the weight loss · The drug’s own contribution barely moved: 11.1 then 11.4. · Everything added between weeks 4 and 26 came from weight. ### Does Semaglutide Help Type 1 Diabetes? What Two Small Trials Found ](https://thisglp.com/research/semaglutide-in-type-1-diabetes)