Semaglutide side effects and risks

Reported side effects

• US boxed warning: thyroid C-cell tumors: Semaglutide caused thyroid C cell tumors in rodents. Whether it causes these tumors in humans is unknown., serious. Avoid with personal or family MTC or MEN2. Report a neck lump, trouble swallowing or persistent hoarseness. (source)
• Nausea: 2.4 mg injection: 44% versus 16% placebo., moderate. Smaller meals and fluids may help; persistent or severe symptoms need review. (source)
• Diarrhea: 2.4 mg injection: 30% versus 16% placebo., moderate. Smaller meals and fluids may help; persistent or severe symptoms need review. (source)
• Vomiting: 2.4 mg injection: 24% versus 6% placebo., moderate. Smaller meals and fluids may help; persistent or severe symptoms need review. (source)
• Constipation: 2.4 mg injection: 24% versus 11% placebo., moderate. Smaller meals and fluids may help; persistent or severe symptoms need review. (source)
• Abdominal pain: 2.4 mg injection: 20% versus 10% placebo., moderate. Smaller meals and fluids may help; persistent or severe symptoms need review. (source)
• Headache: 2.4 mg injection: 14% versus 10% placebo., moderate. Smaller meals and fluids may help; persistent or severe symptoms need review. (source)
• Fatigue: 2.4 mg injection: 11% versus 5% placebo., moderate. Smaller meals and fluids may help; persistent or severe symptoms need review. (source)
• Burping, reflux or indigestion: 2.4 mg: burping 7%, reflux 5%, indigestion 9%; placebo <1%, 3%, 3%., moderate (source)
• Hair loss: 2.4 mg: 3% versus 1% placebo; 7.2 mg: 6% versus 1% placebo., moderate (source)
• Altered or painful skin sensation: Pooled 7.2/2.4 mg/placebo: 22%/6%/0.3%., moderate. Report lasting burning, numbness or painful touch; a dose change may be needed. (source)
• Gallstones: 2.4 mg injection: 1.6% versus 0.7% placebo; oral Wegovy: 2.5% versus 1%., serious (source)
• Gallbladder inflammation: 2.4 mg injection: 0.6% versus 0.2% placebo., serious (source)
• Low blood sugar: Wegovy in diabetes, without insulin: 6.2% versus 2.5% placebo below 54 mg/dL., serious. Risk rises with insulin or sulfonylureas; those medicines may need adjustment. (source)

Stop and get help if

• Severe lasting upper abdominal pain, with or without vomiting: Stop semaglutide and get urgent assessment for pancreatitis.
• Face or throat swelling, breathing trouble or fainting: Stop the drug and call emergency services for possible severe allergy.
• Sudden vision loss or rapidly worsening sight: Get urgent eye care today; confirmed NAION requires stopping semaglutide.
• Confusion, seizure, unconsciousness or low sugar that will not resolve: Call emergency services; severe low blood sugar needs immediate care.
• Repeated vomiting, inability to drink, or very little urine: Get urgent care for dehydration, kidney injury or overdose.
• Severe bloating, vomiting, and no stool or gas: Get urgent care for possible bowel obstruction.
• Right upper abdominal pain with fever, jaundice or pale stool: Get urgent assessment for gallbladder or bile-duct disease.
• Chest pain, fainting or persistent racing heart at rest: Seek urgent care; call emergency services for chest pain or collapse.

Who should avoid it

• mtcOrMen2: US labels contraindicate use with personal or family medullary thyroid cancer or MEN2.
• pregnant: Stop weight-loss use when pregnancy is recognized; diabetes or MASH needs a separate clinician benefit-risk decision.
• tryingToConceive: Stop at least 2 months before planned pregnancy because the drug clears slowly.
• breastfeeding: Oral labels advise against breastfeeding; eight injection users cannot establish infant safety.
• under18: Wegovy injection is also approved for selected ages 12+; this is not a universal pediatric drug contraindication.
• eatingDisorderHistory: Assess nutrition and specialist support.
• other: Do not use after serious allergy to semaglutide or product ingredients.
• pancreatitisHistory: Past pancreatitis needs review. Stop and assess immediately if pancreatitis is suspected.
• gallbladderDisease: Gallstones and gallbladder inflammation can occur, including during rapid weight loss.
• gastroparesis: US labels do not recommend use with severe gastroparesis; review persistent vomiting or very slow stomach emptying.
• diabeticRetinopathy: Rapid glucose improvement can worsen existing diabetic eye disease; arrange eye monitoring.
• kidneyDisease: Dehydration can injure kidneys. US labels do not require routine renal dose adjustment; EU Wegovy restricts severe impairment.
• liverDisease: US labels do not require routine liver dose adjustment. Cirrhosis is outside the approved MASH population.
• heartCondition: Resting heart rate can rise; assess persistent racing, fainting or severe dizziness.
• diabetes: Review glucose medicines and eye history; semaglutide does not replace required insulin.
• surgeryPlanned: Slow stomach emptying can cause aspiration under anesthesia. Tell the team the formulation, dose and last dose date.
• other: Prior NAION needs eye-specialist review; new vision loss needs urgent care. Stop semaglutide if NAION is confirmed.
• depressionOrSuicidalThoughts: Seek help for new suicidal thoughts. FDA found no increased drug-related risk and requested warning removal January 13, 2026.
• testedAthlete: WADA monitors semaglutide markers in and out of competition in 2026; monitoring is not prohibition.

Interactions

• Insulin: Raises low-sugar risk. Insulin changes need glucose-guided adjustment; do not abruptly stop required insulin.
• Sulfonylureas and insulin releasers: These medicines release insulin and can cause low blood sugar with semaglutide.
• Other semaglutide or GLP-1 medicines: Avoid duplicate GLP-1 activity. Wegovy label does not recommend other semaglutide or GLP-1 medicines.
• Levothyroxine: Oral semaglutide increased thyroxine exposure by 33% in a PK study; review timing and thyroid tests.
• Warfarin and coumarins: No important warfarin PK change shown; EU guidance recommends frequent INR checks when starting semaglutide.
• Oral medicines needing close monitoring: Slower stomach emptying may alter absorption. Review drug levels where used; an interaction is not established for every listed drug.
• Oral contraceptives: Tested contraceptive exposure was not reduced. Vomiting or severe diarrhea still needs the pill’s missed-dose advice.
• Other morning tablets with oral semaglutide: Take oral semaglutide first; wait ≥30 minutes before other oral medicines. These tested drugs showed no major PK effect.

Product quality risks

• A 2024 test-purchase study received 3 of 6 online orders. Tested products had 7–14% purity and 29–39% more semaglutide than claimed.
• One sample had elevated endotoxin; no viable microbes were found. A small negative sterility sample does not establish safe production.
• FDA found counterfeit Ozempic in the legitimate US supply chain; authentic lot numbers alone do not prove authenticity.
• FDA reports compounded-vial mistakes of 5–20 times the intended dose. Milligrams, milliliters and syringe units differ.
• Semaglutide sodium and acetate differ from approved semaglutide; FDA does not know that they have the same properties.