Ozempic (semaglutide) carries several well-documented risks, ranging from common gastrointestinal problems that affect the majority of users to rare but serious complications involving the thyroid, pancreas, gallbladder, and kidneys. The most prominent warning on the drug’s label concerns a potential link to thyroid tumors, and roughly 82% of users in clinical trials experienced some form of digestive side effect. Here’s what you should know about each risk before starting or continuing treatment.
The Thyroid Tumor Warning
The most serious caution on Ozempic’s prescribing label is a boxed warning about thyroid tumors. In animal studies, semaglutide caused dose-dependent thyroid C-cell tumors at doses similar to what humans take. Whether this translates to humans remains unknown, but the FDA considered the signal strong enough to require the highest level of warning on the label.
Because of this risk, Ozempic is completely off-limits for anyone with a personal or family history of medullary thyroid carcinoma or a condition called Multiple Endocrine Neoplasia syndrome type 2, which predisposes people to certain endocrine tumors. If you notice a lump in your neck, difficulty swallowing, trouble breathing, or persistent hoarseness while taking Ozempic, those are the specific symptoms to flag immediately.
Gastrointestinal Side Effects
Digestive issues are by far the most common problem. In a two-year clinical trial of semaglutide for weight loss, 82.2% of patients on the drug reported gastrointestinal side effects, compared with 53.9% on placebo. Most of these were mild to moderate: nausea, vomiting, diarrhea, constipation, and abdominal pain. But severe GI reactions do occur. In clinical trials, severe cases were reported in 0.4% to 0.8% of patients depending on dose, compared with 0% on placebo.
The FDA updated Ozempic’s label in October 2025 to strengthen language around severe gastrointestinal reactions, and the drug is now explicitly not recommended for people with severe gastroparesis, a condition where the stomach empties abnormally slowly. The FDA has received reports of gastroparesis developing in semaglutide users, with some cases not resolving even after stopping the medication. Whether the drug directly causes gastroparesis or worsens an underlying tendency hasn’t been confirmed, but the association is concerning enough to warrant the label change.
Surgical Risks From Delayed Stomach Emptying
Ozempic slows down how quickly food leaves your stomach. That’s part of how it reduces appetite, but it creates a specific danger during surgery. There have been reports of patients aspirating (inhaling stomach contents into the lungs) during procedures requiring general anesthesia, even when they followed standard fasting instructions beforehand. The FDA added a new warning about this in January 2025. If you’re scheduled for any surgery or procedure involving sedation, let your medical team know you’re taking Ozempic so they can plan accordingly.
Pancreatitis
Acute pancreatitis, a sudden and painful inflammation of the pancreas, has been reported in less than 1% of patients in major semaglutide trials. It’s rare but can be dangerous. The mechanism appears to involve semaglutide stimulating receptors on pancreatic cells, leading to overgrowth of tissue lining the small ducts of the pancreas and subsequent inflammation. Severe cases, including necrotizing pancreatitis (where pancreatic tissue begins to die), have been documented. The hallmark symptom is intense, persistent abdominal pain that often radiates to the back and doesn’t improve with time.
Gallstones
Rapid weight loss from any cause increases gallstone risk, and semaglutide appears to amplify this further. A systematic review and meta-analysis found that semaglutide increased gallbladder-related disorders, particularly gallstones, by roughly 2.6 times compared to placebo. That’s a 159% increase in risk. Gallstones can be asymptomatic, but when they cause problems, you’ll typically feel sudden, sharp pain in the upper right abdomen, sometimes with nausea or fever if the gallbladder becomes inflamed.
Kidney Injury
Ozempic doesn’t appear to damage the kidneys directly, but it can lead to kidney problems through an indirect route. The nausea, vomiting, and diarrhea it causes can lead to significant fluid loss and dehydration. When you’re dehydrated, your kidneys receive less blood flow, and this can trigger acute kidney injury. The risk is higher if you’re older, already overweight, or taking certain blood pressure medications that also affect kidney function. Monitoring kidney function before starting treatment and throughout is particularly important for people with existing risk factors. Signs to watch for include producing much less urine than usual, swelling in the legs, or unusual fatigue.
Muscle Loss During Weight Loss
One of the less-discussed risks involves body composition. When people lose weight on Ozempic, they don’t just lose fat. Data from the STEP-1 trial showed that out of 15.3 kg (about 34 pounds) of total weight lost, 6.92 kg (about 15 pounds) was lean mass, meaning roughly 45% of the weight lost came from muscle and other non-fat tissue. This significantly exceeds what researchers call the “quarter fat-free mass rule,” which predicts that about 25% of weight loss typically comes from lean tissue.
Losing that much muscle matters, especially for older adults. Muscle loss reduces your metabolic rate (making weight regain easier), weakens your bones, and increases the risk of falls and fractures. Resistance training and adequate protein intake during treatment can help offset this, though the research on how much they can counteract the effect is still evolving.
Vision Changes in People With Diabetes
For people taking Ozempic to manage type 2 diabetes, there’s a specific eye-related risk worth knowing about. When blood sugar drops quickly after a period of being poorly controlled, it can temporarily worsen diabetic retinopathy, a condition affecting blood vessels in the eye. This phenomenon has been recognized since the 1980s and isn’t unique to Ozempic, but semaglutide’s potency at lowering blood sugar makes it relevant. In landmark studies of intensive blood sugar control, 13.1% of patients in the intensive treatment group experienced significant worsening of retinopathy severity at 6 or 12 months, compared with 7.6% in the conventional group. The good news: these changes appear transient and have not been associated with serious or permanent vision loss in studies.
How Dose Titration Reduces Early Risks
Many of Ozempic’s side effects, particularly the GI symptoms, are most intense at the beginning of treatment or after a dose increase. The standard prescribing approach uses a gradual escalation: 0.25 mg weekly for the first four weeks, then 0.5 mg for weeks five through eight, before moving to therapeutic doses of 1.0 mg or 2.0 mg from month three onward. This “start low, go slow” schedule gives your body time to adjust and makes side effects more manageable. Skipping steps or escalating too quickly significantly increases the likelihood and severity of nausea, vomiting, and other digestive problems, which in turn raises the downstream risks of dehydration and kidney stress.