Understanding GLP-1 Side Effects
GLP-1 receptor agonist medications — including semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro) — are generally well-tolerated, but they do cause side effects in a significant proportion of patients, particularly during the initial weeks of treatment and during dose increases. Understanding what to expect can help you manage side effects and stay on track with your treatment.
Last Updated: June 2026
This article provides general information about GLP-1 side effects based on clinical trial data and Health Canada prescribing information. It does not constitute medical advice. Always discuss side effects with your prescribing physician.
Most Common Side Effects
The most frequently reported side effects of GLP-1 medications are gastrointestinal in nature. These include nausea, vomiting, diarrhea, constipation, and abdominal discomfort. In clinical trials for Wegovy, approximately 44% of patients reported nausea, 24% reported diarrhea, and 24% reported vomiting at some point during treatment.
| Side Effect | Frequency (Approx.) | When It Typically Occurs | Duration |
|---|---|---|---|
| Nausea | 40-50% | First 4-8 weeks, after dose increases | Usually improves over time |
| Diarrhea | 20-30% | Early treatment | Usually improves over time |
| Vomiting | 15-25% | First 4-8 weeks | Usually improves over time |
| Constipation | 15-25% | Variable | May persist |
| Abdominal pain | 10-20% | Variable | Usually improves over time |
| Fatigue | 10-15% | Early treatment | Usually improves over time |
| Injection site reactions | 5-10% | Any time | Usually mild and transient |
How to Manage GLP-1 Side Effects
Most gastrointestinal side effects are manageable with practical strategies. Eating smaller, more frequent meals rather than large meals reduces nausea significantly for many patients. Avoiding high-fat, spicy, or heavily processed foods during the first weeks of treatment also helps. Staying well-hydrated is important, particularly if experiencing diarrhea or vomiting. Injecting at night before sleep means many patients sleep through the peak nausea period.
The dose titration schedule — starting at a low dose and increasing gradually over 16 to 20 weeks — is specifically designed to minimize side effects. Do not rush the titration. If side effects are severe at a given dose, discuss with your physician whether to delay the next dose increase.
Side Effects That Require Medical Attention
While most GLP-1 side effects are mild and temporary, certain symptoms require prompt medical attention:
- Severe abdominal pain — particularly pain that radiates to the back, which may indicate pancreatitis
- Persistent vomiting — that prevents adequate fluid intake and may lead to dehydration
- Signs of hypoglycemia — if you are also taking insulin or sulfonylureas, GLP-1 medications can increase the risk of low blood sugar
- Rapid heart rate — GLP-1 medications can cause a modest increase in resting heart rate in some patients
- Vision changes — some patients with type 2 diabetes have reported worsening of diabetic retinopathy
- Lump or swelling in the neck — which may indicate thyroid changes (rare but important to report)
If you experience any of these symptoms, contact your physician or call HealthLink BC at 8-1-1 for guidance.
Who Should Not Take GLP-1 Medications
GLP-1 medications are contraindicated in certain situations. Patients with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN2) should not use these medications. They are also contraindicated during pregnancy and breastfeeding. Patients with a history of pancreatitis should discuss the risks carefully with their physician before starting a GLP-1 medication.
Long-Term Safety
GLP-1 medications have been studied extensively in large cardiovascular outcomes trials. The LEADER trial (liraglutide), SUSTAIN-6 trial (semaglutide), and SELECT trial (semaglutide) all demonstrated cardiovascular safety and, in high-risk populations, cardiovascular benefit. Long-term safety data beyond five years is still accumulating for the newer agents.
You can get a GLP-1 prescription and ongoing medical supervision online in BC through telemedicine providers like Felix without waiting for a GP appointment.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting any medication or if you experience concerning symptoms. For non-emergency health questions, call HealthLink BC at 8-1-1.
Frequently Asked Questions
How long do GLP-1 side effects last?
Most gastrointestinal side effects (nausea, diarrhea, vomiting) are most pronounced during the first four to eight weeks of treatment and during dose increases. For most patients, these side effects improve significantly after the first two to three months as the body adjusts to the medication.
Is nausea from Ozempic or Wegovy permanent?
No. Nausea from GLP-1 medications is typically temporary and most pronounced during the early weeks of treatment. Most patients report significant improvement after the first two to three months. Eating smaller meals and avoiding high-fat foods helps manage nausea during this period.
Can GLP-1 medications cause hair loss?
Some patients report hair shedding (telogen effluvium) during GLP-1 treatment, likely related to rapid weight loss rather than a direct drug effect. This is generally temporary and resolves as weight stabilizes. Adequate protein intake may help minimize hair loss during rapid weight loss.
What is the risk of pancreatitis with GLP-1 medications?
Pancreatitis is a rare but serious potential side effect of GLP-1 medications. The absolute risk is low, but patients should be aware of the symptoms — severe abdominal pain, particularly pain radiating to the back — and seek medical attention promptly if they occur.
Do GLP-1 medications cause muscle loss?
Rapid weight loss from any cause can result in some muscle loss. Clinical trials suggest that GLP-1 medications cause proportionally less lean mass loss than caloric restriction alone, but resistance exercise and adequate protein intake are recommended to preserve muscle mass during treatment.