Feeling worse on tirzepatide or retatrutide: the fine print
The short version: Tirzepatide and retatrutide copy gut hormones, and one of the things those hormones do is slow the stomach down. That explains a lot of the nausea and burping. The rest of the “I feel worse” list, flat days, a faster pulse, hair shedding and gallbladder trouble, is mostly written down in the tirzepatide label and the retatrutide phase 2 trial. Knowing what was reported makes it easier to spot the symptoms that need a doctor.
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The full feeling has a cost
The US label for Zepbound, the weight-loss brand of tirzepatide, says it plainly: tirzepatide delays gastric emptying. Food sits in the stomach longer. A 2025 joint advisory from four US obesity and nutrition societies links that delay to bloating, fullness and nausea, alongside effects on brain areas that control appetite and nausea.
The label pools SURMOUNT-1, the 72-week trial of 2,539 adults without diabetes, with a second trial in people with type 2 diabetes. On the highest dose, 28% reported nausea against 8% on placebo. Burping was 5% against 1%. Across all doses, gut side effects showed up in 56% of people on tirzepatide and 30% on placebo, and most happened while the dose was being stepped up, then eased.
The label adds one more detail. The slowing is biggest after the first dose and fades over time. A 2024 review in the Journal of Clinical Endocrinology and Metabolism describes the same thing for the long-acting drugs in this class.
The joint advisory’s practical advice is food-based: smaller, more frequent meals, and going easy on fatty food in the first days. It notes that vomiting is more likely after large meals, and that skipping food because you feel sick can make the nausea worse.
Flat days and lean mass
When appetite drops this hard, eating too little is easy. The joint advisory warns that low protein intake from reduced appetite can add to muscle loss, and that protein alone is likely not enough without structured resistance training. It also lists fatigue beyond what you’d expect and excessive hair loss among the signs of nutrient shortfall.
The SURMOUNT-1 body scan substudy, published in 2025, analysed DXA scans from 160 people. Of the weight lost on tirzepatide, roughly three quarters was fat and one quarter was lean mass. The detail that rarely gets quoted: the placebo group lost the same split. So the lean loss looks like a feature of losing weight, not of the drug in particular, which is why the advisory leans on protein and lifting.
The advisory adds that severe nausea, vomiting or diarrhoea can dehydrate you enough to cause kidney injury or heart palpitations.
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Retatrutide and your pulse
Retatrutide hits three receptors: GLP-1, GIP and glucagon. In Eli Lilly’s 2022 discovery paper, the glucagon part added extra energy burning on top of eating less, in obese mice.
The phase 2 trial in people, published in the New England Journal of Medicine in 2023, enrolled 338 adults for 48 weeks. Its abstract states that dose-dependent increases in heart rate peaked at 24 weeks and declined after that. The tirzepatide label, by comparison, reports an average rise of 1 to 3 beats per minute, against no rise on placebo.
Those are trial averages. A racing heart that doesn’t settle needs a doctor.
Hair in the shower drain
The tirzepatide label lists hair loss in 5% of people on the highest dose against 1% on placebo, so about 1 in 20 against 1 in 100. It was much more common in women (7.1%) than men (0.5%), the label ties it to weight reduction, and nobody on tirzepatide stopped treatment because of it.
The likely pattern is telogen effluvium, where many hairs switch into their shedding phase at once. A 2019 review in Clinical, Cosmetic and Investigational Dermatology describes the shedding showing up about 3 to 4 months after the triggering event, and names severe dieting and iron deficiency among the triggers. Shedding that runs past six months is classed as chronic, and that is worth a doctor’s visit.
| What people notice | What the source reported | Source |
|---|---|---|
| Nausea | 28% on the highest dose vs 8% on placebo, mostly during dose increases | Tirzepatide label |
| Lean mass loss | About a quarter of weight lost, same share as placebo | SURMOUNT-1 DXA substudy |
| Faster pulse | Up with dose, peaked at week 24, then declined | Retatrutide phase 2 |
| Hair loss | 5% on the highest dose vs 1% on placebo | Tirzepatide label |
| Gallbladder inflammation | 0.7% vs 0.2% on placebo | Tirzepatide label |
The gallbladder part
The label lists acute gallbladder disease under its warnings. In the pooled trials, gallstones were reported in 1.1% of people on tirzepatide and 1% on placebo, gallbladder inflammation in 0.7% against 0.2%, and gallbladder removal in 0.2% against none. The label ties these events to weight reduction.
The US National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) explains why fast weight loss matters: the liver releases extra cholesterol into bile, and the gallbladder may not empty properly. A gallbladder attack usually means pain in the upper right abdomen, often after a heavy meal. NIDDK says to get care right away for pain lasting several hours, fever or chills, or yellowing of the skin or the whites of the eyes.
If you remember one thing: most of these effects were reported in the trials and on the label, but “it’s a known side effect” is not a reason to put up with symptoms that keep building. Severe stomach pain, vomiting that won’t stop or a racing heart need a doctor.
Where the evidence stops
- Trial averages, not your body. A label rate says how common something was in a group, not what is behind your symptoms.
- Retatrutide is earlier in the pipeline. Its heart-rate pattern comes from one phase 2 trial of 338 people over 48 weeks.
- Small substudy. The lean mass figures come from 160 people with scans, not the full trial.
- Licensed medicine only. Every number here comes from pharmaceutical-grade drug given under medical supervision.
A note on framing
Nothing here is advice on using these compounds, and none of it replaces a doctor who knows your history. We have described what the label and trials reported, and when official sources say to get help. We sell to researchers, and we would rather you read the label than a forum thread.
Where JP fits
JP Research supplies Tirzepatide as research-grade freeze-dried powder, for laboratory research use only. Our COA library includes independent Janoshik reports for tirzepatide batches. Orders are dispatched within 1 to 3 business days, with free courier across South Africa. Our reconstitution and storage guide covers handling, and our plain-English guide to peptide terms explains the jargon.
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Sources
- Eli Lilly: Zepbound (tirzepatide) US prescribing information (revised August 2026)
- Jastreboff et al.: Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1, NEJM, 2022)
- Look et al.: Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study (Diabetes Obes Metab, 2025)
- Jastreboff et al.: Triple-hormone-receptor agonist retatrutide for obesity, a phase 2 trial (NEJM, 2023)
- Coskun et al.: LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist (Cell Metab, 2022)
- Mozaffarian et al.: Nutritional priorities to support GLP-1 therapy for obesity, a joint advisory (Obesity, 2025)
- Jalleh et al.: Clinical consequences of delayed gastric emptying with GLP-1 receptor agonists and tirzepatide (J Clin Endocrinol Metab, 2024)
- Rebora: Telogen effluvium, a comprehensive review (Clin Cosmet Investig Dermatol, 2019)
- NIDDK: Dieting and gallstones
- NIDDK: Symptoms and causes of gallstones
All JP Research products are supplied strictly for in-vitro research and laboratory use only. They are not intended for human or animal consumption, medical treatment, or diagnostic use. Nothing in this article constitutes medical advice.