Medicine cautions
Know the common problems and the serious warnings
Stomach trouble is common. A few less common problems need fast attention, and the official label rules the medicine out for some people.
Feeling sick is the most common side effect
In the Wegovy weight trials, nausea was much more common with semaglutide than with a dummy shot.
Diarrhea, vomiting, constipation, and stomach pain were also common. The diabetes trials used lower strengths and reported lower rates.
Severe stomach trouble can affect the kidneys
Vomiting or diarrhea can cause a large fluid loss. The label reports kidney injury, including cases that needed dialysis.
The Wegovy label does not recommend the medicine for people with severe gastroparesis. That condition means the stomach empties very slowly.
Gallbladder and pancreas problems are in the label
Gallstones and gallbladder inflammation were more common with semaglutide in the weight trials.
Inflammation of the pancreas has also been reported. The label describes severe stomach pain that may spread to the back and does not go away.
The boxed warning is about thyroid tumors
Every approved semaglutide label carries the FDA’s strongest warning type, called a boxed warning.
Semaglutide caused thyroid tumors in rats and mice. It is not known whether it causes those tumors in people.
Medullary thyroid cancer is a rare cancer that starts in specific thyroid cells. The label rules the medicine out for someone with that cancer in their personal or family history. If an older family diagnosis is unclear, ask what type of thyroid cancer it was. It also rules the medicine out for MEN 2.
MEN 2 is a rare inherited condition that raises the chance of tumors in certain glands.
Pregnancy and surgery belong in the first review
The Wegovy label tells people who write prescriptions to stop it at least two months before a planned pregnancy.
The label also warns about food left in the stomach during surgery or a procedure using deep sedation or general anesthesia. Deep sedation means medicine leaves you barely responsive.
It says patients need to tell the surgery or procedure team they take Wegovy. The label says there is not enough evidence to know whether stopping it beforehand lowers that risk, so ask that team what to do and do not stop it on your own.
Other health details can change the plan
A careful review asks about past pancreas or gallbladder trouble, serious stomach problems, diabetic eye disease, and allergic reactions.
It also covers other diabetes medicines, pregnancy plans, kidney problems, and any surgery coming up.
A service should ask about these health details instead of only letting you choose a medicine from a menu.
Made-to-order products need extra checks
Medicine made to order by a pharmacy or doctor is called compounded medicine. As of September 2026, compounded semaglutide was not FDA-approved. The FDA did not check each batch before it was marketed.
The FDA received reports of dose mistakes with compounded injections. Some people needed hospital care.
Labels stated medicine strength in different ways. Patients or medical professionals sometimes measured or calculated the wrong amount. Ask the pharmacy to show you which syringe markings match its written directions. This guide gives no dose or unit conversion.
The pharmacy name on the label can be checked with a state board of pharmacy.
When help cannot wait
A severe allergic reaction can start within seconds or minutes. Trouble breathing, face or tongue swelling, fainting, or widespread hives can be emergency signs.
Call emergency services for a severe allergic reaction.
For a medicine mistake or wrong amount, Poison Control offers free and private help online or by phone all day and night.