Scientific deep-dive
Which GLP-1 Has the Worst Side Effects?
A network meta-analysis of 33,354 people ranks the drugs symptom by symptom. Orforglipron, the oral pill, tops the nausea ranking, ahead of every injection.
Every GLP-1 causes gastrointestinal side effects, and until recently there was no way to compare them properly. A network meta-analysis of 33,354 adults with overweight or obesity and without diabetes now ranks them — and the drug with the highest nausea risk is the one people assume will be gentlest: orforglipron, the oral pill.[1]
The rankings
| Symptom | Which drugs raised the risk | Which did not |
|---|---|---|
| Nausea | All of them. Highest orforglipron, then exenatide, tirzepatide, semaglutide, liraglutide | — |
| Vomiting | Liraglutide, orforglipron, semaglutide, tirzepatide | Cagrilintide, exenatide |
| Diarrhea | Others in the analysis | Exenatide, cagrilintide, orforglipron |
| Constipation | Semaglutide, liraglutide, tirzepatide, orforglipron (see correction below) | Cagrilintide, exenatide |
Nausea, vomiting, diarrhea and constipation were the most common gastrointestinal effects across the board, which will surprise nobody taking one. What is new is being able to say which drug is worse for which symptom.[1]
The oral pill is not the gentle option
The assumption that swallowing it instead of injecting it will be easier on the stomach is the opposite of what the data show.
Orforglipron came top for nausea and was among the drugs raising vomiting risk. That matters because it is the first approved oral non-peptide in this class and it is being marketed heavily on the convenience of a tablet — see our Foundayo article. Convenience of administration and gentleness on the gut are separate properties, and here they point in opposite directions.
In this analysis orforglipron was not associated with increased diarrhea risk. A drug can rank badly on one symptom and well on another, which is exactly why a single “tolerability” verdict is unhelpful.
How to use a ranking like this
- Match it to your own worst symptom. If constipation is what stopped you before, switching may not solve it: tirzepatide and the oral pill raise it too, and the constipation guide covers what helps. If vomiting is the problem, the picture is different again.
- Do not read it as a dose-matched comparison. Each drug was tested at its own doses in its own trials. A ranking of drugs is not a ranking of molecules at equivalent exposure.
- This is a non-diabetic population, deliberately. Rates and rankings differ in diabetes trials, where patients are often on other gastrointestinal-active drugs.
- Weight loss and side effects travel together. The drugs that do most tend to cause most, and a ranking that ignored efficacy would mislead.
Frequently Asked Questions
References
- 1.Ismaiel A, Scarlata GGM, Boitos I, et al. Gastrointestinal adverse events associated with GLP-1 RA in non-diabetic patients with overweight or obesity: a systematic review and network meta-analysis International Journal of Obesity. 2025. PMID: 40804463.
- 2.Eli Lilly and Company FOUNDAYO (orforglipron) tablets — prescribing information (section 6.1, Table 1) DailyMed, U.S. National Library of Medicine. 2026. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=8ac446c5-feba-474f-a103-23facb9b5c62
- 3.Eli Lilly and Company ZEPBOUND (tirzepatide) injection — prescribing information (section 6.1, Table 1) DailyMed, U.S. National Library of Medicine. 2026. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=487cd7e7-434c-4925-99fa-aa80b1cc776b
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Oral orforglipron alongside the injectables
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