Semaglutide: what it treats, how to use it, side effects
Last updated September 3, 2026.
Semaglutide is a GLP-1 medication - a weekly injection that mimics a gut hormone to lower blood sugar and quiet appetite. You may know it as Ozempic for type 2 diabetes; the same molecule treats weight and liver disease under other brand names. It carries a boxed warning about thyroid tumors, and it starts low and climbs slowly for a reason.
What does it treat?
Per MedlinePlus: blood sugar control in type 2 diabetes; reducing the risk of heart attack, stroke, and death in adults with type 2 diabetes and heart and blood vessel disease, and in adults who are obese or overweight with heart and blood vessel disease; reducing the risk of worsening kidney disease and death in certain adults with type 2 diabetes and kidney disease; weight loss in certain people who are obese or overweight with weight-related medical problems; and noncirrhotic MASH, a liver disease. It is not for type 1 diabetes.
How do you use it?
One injection under the skin once a week, on the same day each week, at any time of day, with or without meals. You can change the weekly day as long as at least 2 days have passed since the last dose. The label starts everyone at 0.25 mg once weekly for 4 weeks - a get-used-to-it dose - then rises to 0.5 mg, with further increases to 1 mg or 2 mg no sooner than every 4 weeks based on response. Inject into the abdomen, thigh, or upper arm, rotating sites. Look at the liquid every time: clear, colorless, no particles, not past the pen's expiration. Never reuse or share needles or pens, never mix it with insulin in one syringe, and pull the needle off right after injecting. Keep the pens in the refrigerator, never frozen; room-temperature storage has a time limit - ask your pharmacist for yours. Missed dose for diabetes: inject it as soon as you remember within 5 days; past 5 days, skip it and never double up.
Side effects to know
- Common: nausea, vomiting, diarrhea, stomach pain, constipation, heartburn, burping, runny nose or sore throat, and headache. The stomach effects are worst at the start and after each dose increase.
- Serious - call your doctor immediately or get emergency care: ongoing pain that begins in the upper left or middle of the stomach and may spread to the back, with or without vomiting (pancreatitis); allergic reactions with rash, itching, fainting or dizziness, swelling of the eyes, face, mouth, tongue, or throat, or trouble breathing or swallowing; decreased urination or swelling of the legs, ankles, or feet (kidneys); vision changes; pain in the upper stomach with yellowing of the skin or eyes, fever, or clay-colored stools (gallbladder); a rapid or pounding heartbeat; and severe stomach or intestinal problems.
Who should not use it?
The boxed warning: semaglutide caused thyroid tumors in rats, and whether it raises tumor risk in humans is unknown. Anyone with a personal or family history of thyroid tumors, thyroid cancer, or Multiple Endocrine Neoplasia syndrome type 2 will probably be told not to use it - and a lump or swelling in the neck, hoarseness, trouble swallowing, or shortness of breath on the drug means calling your doctor immediately. Flag past pancreatitis, diabetic retinopathy, severe stomach problems including gastroparesis, gallbladder disease, and kidney disease, plus any recent vomiting, diarrhea, or inability to drink fluids. Planning a pregnancy: MedlinePlus says your doctor will tell you to stop semaglutide 2 months before a planned pregnancy. If you also take insulin or a sulfonylurea, low blood sugar becomes possible - know the symptoms.
When is it an emergency?
Trouble breathing or swallowing, or swelling of the face, tongue, or throat, is a 911 call. Severe stomach pain spreading to your back with vomiting means immediate care. So does a severe low blood sugar - confusion, inability to wake, seizure - if you combine it with insulin or a sulfonylurea. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why does semaglutide start at such a low dose?
Your stomach needs time. The label starts everyone at 0.25 mg once weekly for 4 weeks, then moves to 0.5 mg, with any further increases at least 4 weeks apart - the slow climb exists to limit the nausea, vomiting, and diarrhea this class is known for. The starting dose is a ramp, not the destination.
What is the thyroid warning about?
The boxed warning on the label: semaglutide caused thyroid gland tumors, including a type of thyroid cancer, in rats, and it is not known if the risk carries to humans. Anyone with a personal or family history of thyroid cancer or MEN 2 syndrome will probably be told not to use it. On the drug, a lump or swelling in the neck, hoarseness, trouble swallowing, or shortness of breath means calling your doctor immediately.
Why do I have to stop semaglutide before a planned pregnancy?
MedlinePlus is specific: if you plan to become pregnant, your doctor will tell you to stop semaglutide 2 months before the planned pregnancy - the drug needs time to clear. If you become pregnant while using it, call your doctor immediately. This belongs in the first conversation, not after a positive test.
What happens if I miss my semaglutide dose?
For diabetes, inject it as soon as you remember within 5 days of the missed dose. More than 5 days gone, skip it and take the next one on your regular day - never double up. The once-weekly rhythm is forgiving about a day or two; the 5-day line is the hard rule.
Can I drink alcohol while using semaglutide?
Neither the label nor MedlinePlus gives semaglutide-specific alcohol language. Alcohol can swing blood sugar in people with diabetes, and it irritates the same stomach the drug is already working on. Keep it light and get the explicit rule from your doctor.
Why does everyone talk about nausea with this injection?
Because it slows the stomach - that is part of how it works. MedlinePlus lists nausea, vomiting, diarrhea, stomach pain, and constipation as the common effects, worst in the first weeks and after each dose step. Most people adapt. Ongoing severe stomach problems, or pain spreading to your back, cross the line from expected to call-your-doctor-immediately.