Everything published about CT-388's side effects amounts to one sentence: adverse events were generally well tolerated, most were mild or moderate, and the profile was consistent with other incretin-based drugs. There are no percentages, no dose columns, no discontinuation rate. If you have found a table of CT-388 side effect frequencies somewhere, it was not taken from a trial of CT-388.
What the trial actually reported
One clinical study has been published: a phase 1, randomised, placebo-controlled trial in otherwise healthy participants with overweight or obesity, running 29 days, testing single doses of 0.5 to 7.5 mg and four weekly doses of 5 to 12 mg.
On safety it states three things:
- CT-388 was generally well tolerated.
- The safety profile was consistent with other incretin-based therapies.
- Most treatment-emergent adverse events were mild or moderate.
That is the complete record. For comparison, Zepbound's label lists sixteen adverse reactions with incidence by dose against placebo, and Foundayo's lists thirteen.
Why the gap exists
Incidence tables are produced for regulatory approval. A manufacturer submits its full safety database, the regulator reviews it, and the agreed figures appear in the label. CT-388 has not been through that, so no such table exists to publish.
What a phase 1 report gives instead is a summary judgement, because phase 1 is designed to establish whether a dose is tolerable at all rather than to quantify how often each symptom occurs. Twenty-nine days in a small cohort of healthy volunteers is not a dataset that supports percentages anyone should rely on.
What "consistent with other incretin-based therapies" commits to
It is a specific phrase, not a vague reassurance, and it is worth unpacking.
The incretin class — semaglutide, tirzepatide, orforglipron — has a well-characterised profile: gastrointestinal effects dominate, they are dose-related, they cluster during dose escalation, and they ease with continued treatment. Nausea runs anywhere from 28% to 44% at maintenance doses depending on the molecule.
Saying CT-388 looked consistent with that means the trial saw the same kind of thing rather than a surprise. It does not mean the rates match any particular drug. Within that same class, Mounjaro reports 18% nausea and Wegovy 44% — a spread wide enough that "consistent with the class" narrows very little.
What would be reasonable to expect
Reasonable to expect, not established:
- Gastrointestinal effects predominating — nausea, vomiting, diarrhoea, constipation. Every drug at these receptors produces them.
- Dose-dependence, with a titration schedule designed around it.
- Worst during escalation, easing afterwards.
- The class warnings — thyroid C-cell tumours from rodent studies, pancreatitis, gallbladder disease — appearing on any eventual label, since these attach to the receptor family rather than to individual molecules.
None of that is CT-388 data. It is what the class does, offered as context rather than as an answer.
The one thing that might genuinely differ
CT-388's design is unusual, and if it works it could change the side effect profile rather than just the efficacy.
It is engineered as a signalling-biased agonist: it drives the receptors' signal while causing minimal internalisation, the process by which a stimulated receptor is pulled inside the cell. Receptor internalisation and desensitisation are part of how the body adapts to these drugs, and adaptation is part of why side effects ease over time.
A drug that deliberately avoids that adaptation might produce a different tolerability curve — better or worse. Nobody has published data either way, and four weeks is far too short to see it. It is a reason the eventual phase 3 safety data will be worth reading rather than assuming.
What this means practically
CT-388 cannot be prescribed, so nobody is weighing its side effects against an alternative in a clinic. The practical value of this page is negative knowledge: if you encounter a specific percentage attached to CT-388, it did not come from a CT-388 trial.
What the molecule is and what it has shown is in the CT-388 overview; the efficacy figure and its four-week caveat in CT-388 weight loss. For drugs with complete published safety data, see Foundayo side effects or tirzepatide side effects.
The rest of the set
What is CT-388, CT-388 weight loss, and the comparisons: vs Wegovy and vs Ozempic.
Scientific References
2 sources- 1
Chakravarthy MV, Rodriguez R, Hergarden A, et al.
Effects of CT-388, a once-weekly signaling-biased dual GLP-1/GIP receptor agonist, on weight loss and glycemic control in preclinical models and participants with obesity
Molecular Metabolism · 103 · 2026PMID: 41319798
NIH - 2
Eli Lilly and Company
ZEPBOUND (tirzepatide) and MOUNJARO (tirzepatide) — Prescribing Information, §6.1 adverse reaction tables, cited for class context
DailyMed, U.S. National Library of Medicine · 2026
NIH
References open in a new tab. Content is reviewed against peer-reviewed literature as part of our editorial policy.
About the author
Editor, Modern Weight Science
Claudiu Gheorghe is the editor of Modern Weight Science. He is not a physician. His role is to synthesize peer-reviewed studies, clinical-trial data, and FDA prescribing information into clear, plain-language explanations, and to make sure every factual claim on the site traces back to a cited source. Any decision about starting, changing, or stopping a medication belongs with a licensed clinician who knows your history.
Every claim is checked against peer-reviewed research through our review process and fact-checking policy.
Frequently Asked Questions
What are the side effects of CT-388?
Unknown in any quantified sense. The one published trial states that CT-388 was generally well tolerated, that most treatment-emergent adverse events were mild or moderate, and that the profile was consistent with other incretin-based therapies. There are no incidence percentages, no breakdown by dose and no discontinuation rate.
Why are there no CT-388 side effect percentages?
Because incidence tables are produced for regulatory approval, and CT-388 has not been approved. A phase 1 trial is designed to establish whether a dose is tolerable at all, not to quantify how often each symptom occurs, and 29 days in a small cohort of healthy volunteers does not support percentages anyone should rely on.
Is CT-388 safer than Zepbound?
There is no basis for saying so in either direction. Zepbound has a full label with sixteen adverse reactions reported by dose against placebo; CT-388 has one summary sentence. Its design might plausibly produce a different tolerability curve — it is engineered to avoid the receptor internalisation that normally accompanies these drugs — but no data tests that.
Does CT-388 cause nausea?
Almost certainly, since every drug acting at these receptors does, and the trial described its profile as consistent with other incretin therapies. How often is not published. Within that class the range is wide — 18% on Mounjaro to 44% on Wegovy — so 'consistent with the class' does not narrow the answer much.
I found a table of CT-388 side effect rates. Is it real?
It did not come from a CT-388 trial, because no such figures have been published. It has most likely been borrowed from tirzepatide or another drug in the class and presented as indicative. Treat any specific percentage attached to this molecule as unsourced.
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Where to read next
Not medical advice. This guide is for general education only. GLP-1 medications, dosing, and treatment suitability are decisions for you and a licensed clinician who knows your full medical history.