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Semaglutide works partly by slowing your stomach and quieting your appetite [1]. So it makes sense that most of its side effects show up in your gut. For many people they are a phase, not the whole story. But a few side effects need quick attention, and it helps to know which ones.
The numbers below come from the FDA-approved semaglutide label for weight management. Most come from three placebo-controlled trials that included 2,116 adults on semaglutide 2.4 mg for up to 68 weeks [1]. Their average age was 48, and 71% were women [1].
The most common side effects
| Side effect | Semaglutide 2.4 mg | Placebo |
|---|---|---|
| Nausea | 44% | 16% |
| Diarrhea | 30% | 16% |
| Vomiting | 24% | 6% |
| Constipation | 24% | 11% |
| Stomach (abdominal) pain | 20% | 10% |
| Headache | 14% | 10% |
| Fatigue | 11% | 5% |
| Indigestion | 9% | 3% |
| Dizziness | 8% | 4% |
| Bloating | 7% | 5% |
| Burping | 7% | Less than 1% |
| Gas | 6% | 4% |
| Acid reflux (GERD) | 5% | 3% |
| Hair loss | 3% | 1% |
Notice the placebo column. People taking no drug at all also reported nausea, headaches and tiredness. The difference between the two columns is the part linked to the medicine.
Nausea and other stomach side effects
In the weight trials, 73% of people on semaglutide and 47% on placebo reported a digestive side effect [1]. The label says these were reported most often during dose escalation, the weeks when the dose is being stepped up [1]. In the STEP 1 trial, nausea and diarrhea were the most common side effects, and they were typically short-lived, mild to moderate, and eased with time [2].
Some people do stop. In the weight trials, 4.3% of people on semaglutide stopped the medicine for good because of a digestive side effect, compared with 0.7% on placebo [1]. Severe digestive side effects were reported by 4.1% on semaglutide and 0.9% on placebo [1].
The label also lists rarer gut problems reported after approval: blocked bowel (ileus or intestinal obstruction) and severe constipation, including stool that gets stuck [1]. Semaglutide is not recommended for people with severe gastroparesis, a condition where the stomach empties very slowly [1].
Dehydration and your kidneys
Vomiting and diarrhea can dry you out. The label reports cases of acute kidney injury, some needing dialysis, mostly in people who became dehydrated from digestive side effects [1]. The patient guide says it is important to drink fluids, and to tell your clinician right away about nausea, vomiting or diarrhea that does not go away [1].
Other side effects to know about
- Hair loss. Reported by 3.3% on semaglutide 2.4 mg and 1% on placebo, and more often in women (4%) than men (0.9%) [1]. The label links it to weight reduction [1].
- Skin that feels different. Tingling, burning, or skin that is sensitive or painful to touch (the label calls this dysesthesia). It became more common as the dose went up: 6% on 2.4 mg and 22% on the higher 7.2 mg dose, compared with 0.3% on placebo [1].
- Faster heart rate. Resting heart rate rose by 1 to 4 beats per minute on average compared with placebo [1]. Tell your clinician if you feel your heart racing while you are resting [1].
- Low blood pressure and fainting. Low blood pressure was reported by 1.3% on semaglutide and 0.4% on placebo, and fainting by 0.8% and 0.2% [1]. Some cases were tied to fluid loss, and they were more common in people taking blood pressure medicines [1].
- Changes in taste. Reported by 1.7% on semaglutide and 0.5% on placebo [1].
- Injection site reactions. Itching, redness or swelling where you inject, reported by 1.4% on semaglutide and 1% on placebo [1].
Serious risks, and the boxed warning
These are less common. They are the reason a clinician reviews your history before prescribing.
Thyroid C-cell tumors (boxed warning)
In mice and rats, semaglutide caused thyroid C-cell tumors. It is not known whether it does this in people [1]. Because of that, semaglutide should not be used if you or a family member has had medullary thyroid carcinoma (MTC), or if you have multiple endocrine neoplasia type 2 (MEN 2) [1]. Tell your clinician about a lump in your neck, trouble swallowing, shortness of breath, or hoarseness that will not go away [1].
Pancreatitis
Inflammation of the pancreas has been seen with GLP-1 medicines, including semaglutide [1]. In the weight trials it was confirmed in 4 people on semaglutide and 1 on placebo [1]. The warning sign is severe stomach pain that will not go away, sometimes spreading to your back, with or without vomiting. If that happens, stop the medicine and call your clinician right away [1].
Gallbladder problems
Gallstones were reported by 1.6% of adults on semaglutide injection and 0.7% on placebo. Gallbladder inflammation was reported by 0.6% and 0.2% [1]. Fast weight loss can raise the risk of gallstones, but the label says the risk was higher on semaglutide even after accounting for weight lost [1]. Watch for pain in your upper stomach, fever, yellow skin or eyes, or clay-colored stools [1].
Other warnings on the label
- Serious allergic reactions, including swelling of the face, lips, tongue or throat. Get help right away [1].
- Low blood sugar, mainly if you also take insulin or a sulfonylurea for diabetes [1].
- Eye changes in people with type 2 diabetes who already have diabetic retinopathy [1].
- Anesthesia and surgery. Because semaglutide slows the stomach, food in the lungs has been reported during procedures with anesthesia or deep sedation. Tell every clinician about semaglutide before a planned procedure [1].
- Bone fractures. In a large heart outcomes trial, more women on semaglutide than on placebo had hip and pelvis fractures: 1% compared with 0.2% [1].
- Pregnancy. Semaglutide may harm an unborn baby. The label says to stop it at least 2 months before a planned pregnancy [1].
What helps, according to the label
The label does not promise a way to avoid side effects. It does describe how the medicine is meant to be started and adjusted to lower the risk.
- Take it once a week, on the same day
- Drink fluids if you have nausea, vomiting or diarrhea
- Report side effects that are severe or will not go away
- Tell every clinician before a procedure with anesthesia
- Starts low and raises the dose every 4 weeks
- Waits longer before the next step if a dose is hard to tolerate
- Restarts at a lower dose after 2 or more missed doses
- Checks your kidneys if you lose a lot of fluid
The slow start is the main tool. The label starts semaglutide at 0.25 mg a week for 4 weeks, then steps up every 4 weeks to the maintenance dose. It says this schedule is meant to reduce the risk of digestive side effects [1]. If you do not tolerate a step, the label says your clinician may delay the next increase by 4 weeks [1].
Missed doses matter too. If you miss 2 or more weekly doses in a row, the label says to restart at a lower dose, again to reduce digestive side effects [1]. Do not simply jump back in at your old dose without asking.
Your other medicines. Semaglutide slows how fast your stomach empties, which may change how some pills are absorbed [1]. Give your clinician a full list of what you take.
To see how these side effects compare with tirzepatide's, read semaglutide vs tirzepatide.
Semaglutide at WarriorBabe Health
WarriorBabe Health offers semaglutide injections and a semaglutide tablet, prescribed and monitored by licensed clinicians who review your history first. Ours are compounded by a licensed pharmacy and are not FDA-approved. The FDA does not review compounded drugs for safety, effectiveness or quality before they are sold [3]. It has also received reports of side effects linked to dosing mistakes with compounded semaglutide, such as measuring the wrong amount [3]. Ask your clinician or pharmacist to walk you through your exact dose.
Frequently asked questions
How long do semaglutide side effects last?
The label says digestive side effects were reported most often while the dose was being raised [1]. In STEP 1, nausea and diarrhea were typically short-lived and eased with time [2]. Everyone is different, so tell your clinician about side effects that are severe or do not go away.
Does semaglutide cause hair loss?
Hair loss was reported by 3.3% of people on semaglutide 2.4 mg and 1% on placebo, and more often by women [1]. The label links it to weight reduction [1].
What are the serious side effects of semaglutide?
The label warns about pancreatitis, gallbladder problems, kidney injury from dehydration, serious allergic reactions, low blood sugar with some diabetes medicines, and food in the lungs during anesthesia. It also carries a boxed warning about thyroid C-cell tumors seen in rodents [1].
Why does semaglutide make me feel sick?
Semaglutide slows how quickly your stomach empties and reduces appetite [1]. Nausea was the most common side effect in the weight trials, reported by 44% on semaglutide and 16% on placebo [1].
Who should not take semaglutide?
The label says not to use it if you or a family member has had medullary thyroid carcinoma, if you have MEN 2, or if you have had a serious allergic reaction to semaglutide [1]. It is not recommended with severe gastroparesis, and it should be stopped during pregnancy [1].
References
- Novo Nordisk. Wegovy (semaglutide) injection and tablets, prescribing information. DailyMed, US National Library of Medicine. Revised 6/2026. dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ee06186f-2aa3-4990-a760-757579d8f77b
- Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989-1002. pubmed.ncbi.nlm.nih.gov/33567185/
- US Food and Drug Administration. FDA's concerns with unapproved GLP-1 drugs used for weight loss. www.fda.gov/drugs/drug-alerts-and-statements/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss
This article is for general information. It is not medical advice and does not replace a visit with a licensed clinician who knows your history. Do not start, stop or change a medication without talking to your clinician. If you think you are having a medical emergency, call 911.
