Quick answer
As of September 26, 2026, the most common side effects of GLP-1 medications such as semaglutide and tirzepatide are gastrointestinal: nausea, vomiting, diarrhea, constipation and abdominal pain. Management is practical: smaller meals, fewer fatty foods, steady fluids, and a treatment plan your physician reviews with you. Call a clinician promptly for severe abdominal pain, persistent vomiting, signs of gallbladder disease, vision changes or an allergic reaction, all of which the labels list as warnings. Compounded medications are not FDA-approved as final products.
Starting any new medication comes with questions. One of the most common concerns about GLP-1 weight loss medications is side effects, and that's a perfectly reasonable thing to ask.
Most of the common side effects are gastrointestinal, and there are practical ways to reduce them. Knowing what to expect and how to handle it makes the experience smoother, and your care team is there for anything that does not settle.
Why Do Side Effects Happen?
GLP-1 medications work by slowing down your digestion and signaling your brain that you're full. The same mechanisms can also cause digestive discomfort.
The Most Common Side Effects
Nausea
Nausea is a commonly reported side effect.
*How to manage it:*
- Eat smaller, more frequent meals rather than a few large ones
- Avoid fatty, greasy, or heavily spiced foods
- Stick with bland options like crackers, toast, rice, or bananas
- Stay hydrated, but sip water slowly
- Eat slowly and stop when you feel satisfied
If nausea persists or stops you eating and drinking, tell your care team.
Constipation
Because GLP-1 medications slow gastric emptying, food moves through your digestive tract more slowly.
*How to manage it:*
- Drink plenty of water through the day
- Increase fiber with vegetables, fruits, whole grains, and legumes
- Stay active, even a short walk helps stimulate digestion
- Consider a gentle fiber supplement (talk to your doctor first)
Diarrhea
Some people experience loose stools or diarrhea.
*How to manage it:*
- Stay well-hydrated to replace lost fluids
- Eat binding foods like bananas, rice, applesauce, and toast
- Avoid dairy, caffeine, and high-fiber foods until it passes
- Contact your doctor if it persists beyond a few days
Fatigue
Some patients feel more tired than usual.
*How to manage it:*
- Give yourself permission to rest
- Prioritize sleep
- Stay hydrated
- Light exercise like walking can boost energy levels
Headache and Dizziness
Occasional headaches can occur.
*How to manage it:*
- Drink plenty of water
- Consider over-the-counter pain relief (consult your doctor first)
- Eat regularly, low blood sugar can cause headaches too
Injection Site Reactions
You may notice redness, swelling, or itching at the injection site.
*How to manage it:*
- Rotate injection sites (abdomen, thigh, upper arm)
- Apply a cold compress if there's swelling
- Do not rub or massage the injection site
When Should You Call Your Doctor?
Contact your healthcare provider if you experience:
- Severe or persistent nausea/vomiting preventing you from keeping fluids down
- Signs of pancreatitis, severe abdominal pain that radiates to your back
- Symptoms of gallbladder issues, severe upper right abdominal pain, fever, or jaundice
- Significant changes in vision
- Signs of an allergic reaction, difficulty breathing, swelling of the face or throat
- New or worsening mood changes, which you should always report to your care team; if you have thoughts of harming yourself, seek help immediately
Tips for a Smoother Start
- Follow the schedule on your pharmacy label, set by your prescriber
- Prescribing information for the approved products allows the injection with or without meals; if you notice a pattern with nausea, tell your care team
- Hydrate before, during, and after, dehydration amplifies side effects
- Avoid trigger foods and stick with simple, whole foods while you settle in
- Get ahead of constipation, increase fiber and water from day one
- Communicate early, if side effects bother you, tell your care team
What to Keep in Mind
Tell your care team about anything that persists or worsens; your physician can review your treatment plan. Individual results may vary.
Considering treatment? Start the medical assessment at /quiz. A licensed physician reviews your information, and medication is prescribed only if a licensed physician determines it is appropriate.
What the primary sources say
- DailyMed, semaglutide injection prescribing information, section 2 (accessed September 26, 2026): "Follow the dosage escalation in Table 1 to reduce the risk of gastrointestinal adverse reactions"
- DailyMed, tirzepatide injection prescribing information, section 6.1 (accessed September 26, 2026): "The majority of nausea, vomiting, and/or diarrhea events occurred during dose escalation and decreased over time."
- MedlinePlus, Tirzepatide Injection (accessed September 29, 2026): "Tirzepatide can be injected in the abdomen, thigh or upper arm. Rotate injection sites with each dose."
- MedlinePlus, Semaglutide Injection (accessed September 26, 2026): "Also tell your doctor if you have recently had diarrhea, nausea, or vomiting or if you cannot drink liquids by mouth, which may cause dehydration (loss of a large amount of body fluids)."
- MedlinePlus, Constipation - self-care (accessed September 26, 2026): "You can get constipated if you do not get enough fiber, drink enough water, or get enough exercise."
This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider. Compounded medications are not FDA-approved as final products. Medication is prescribed only if a licensed physician determines it is appropriate. Individual results may vary.
Related 2026 guides
Frequently Asked Questions
How do you manage nausea on GLP-1 medications?
Practical steps that help most patients: eat smaller portions and stop at the first sign of fullness, avoid high-fat or fried foods which prolong gastric emptying, hydrate steadily through the day separated from meals, limit alcohol, and eat protein early in the meal. If nausea is significant or interferes with daily life, tell your physician, who can review your treatment plan and discuss options with you.
How do you treat constipation on GLP-1 medications?
Three pillars: hydration (drink more water through the day), fiber (from vegetables, beans, whole grains, and chia or flax seeds), and movement (daily walking and light activity). If those are not enough, stool softeners are sold at any pharmacy, and your physician may prescribe a laxative if needed. Stimulant laxatives are reserved for short-term use and are not a long-term solution.
When should I call my doctor about GLP-1 side effects?
Contact your physician immediately for severe abdominal pain (especially radiating to the back, possible pancreatitis), persistent vomiting or inability to keep fluids down (dehydration risk), right-upper-quadrant pain with fever or jaundice (possible gallbladder disease), unusual swelling of the face or throat or hives (possible allergic reaction), vision changes (especially in patients with diabetes), and symptoms of low blood sugar in patients also on insulin or sulfonylureas. Mild to moderate gastrointestinal side effects that worsen instead of improving also warrant a check-in.
How long do GLP-1 side effects last?
There is no fixed duration that applies to everyone. Smaller portions and steady fluids help. Side effects that persist, or that worsen instead of improving, signal that the current plan needs physician review.
What is the worst week for GLP-1 side effects?
There is no single week that applies to everyone. For a compounded preparation, the schedule is on the pharmacy label and set by the prescriber; tell your care team if side effects do not settle.
Does it matter where I inject a GLP-1 medication?
Yes, within the sites the label allows. The FDA-approved labels for the injectable products direct patients to inject under the skin of the abdomen, the thigh or the upper arm, and to rotate sites from one dose to the next. Rotating is what the labels direct; redness, swelling or itching where you inject is a reason to check that you are not reusing the same spot. Follow the site instructions on your own prescription label and Medication Guide, and tell your care team if a reaction does not settle.
Sources
This article is based on the following primary sources. Links open the original documents.
- 1.DailyMed - semaglutide injection, solution; semaglutide tablet (Prescribing Information, Revised 6/2026) · U.S. National Library of Medicine, DailyMed (FDA-approved labeling, the manufacturer) · accessed
- 2.DailyMed - tirzepatide injection, solution (Prescribing Information, Revised 8/2026) · U.S. National Library of Medicine, DailyMed (FDA-approved labeling, the manufacturer) · accessed
- 3.Semaglutide Injection: MedlinePlus Drug Information (Last Revised 05/15/2026) · MedlinePlus, U.S. National Library of Medicine (NIH) · accessed
- 4.Constipation - self-care: MedlinePlus Medical Encyclopedia (Review Date 7/15/2024) · MedlinePlus, U.S. National Library of Medicine (NIH) · accessed
- 5.Tirzepatide injection (drug information, last revised 02/15/2026) · American Society of Health-System Pharmacists (AHFS), via MedlinePlus · accessed
Is this available in your state?
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Majesta Health articles are written against primary sources (FDA labeling, NIH and CDC publications, state statutes) and each one passes a documented compliance review before publication. Where an article cites external sources, they are listed at the end of that article so you can check them yourself. No article currently carries an individual physician review; when a physician reviews an article, that page will show the reviewer's name, NPI and review date.
- Written against primary sources: FDA labeling and safety communications, NIH and CDC publications, state statutes and medical board rules
- Documented compliance review against FDA, FTC and LegitScript requirements before publication
- External sources, where an article cites them, are listed at the end of that article with links to the original documents
- Compounded medications are described as not FDA-approved as final products on every page that mentions them