FGuide F of 7 Last reviewed: September 2026
Side effects and who should not take GLP-1s
This is the guide to read twice. It is written at the pattern level from the medications' labeling and does not replace the prescribing information or your clinician's judgment.
Common side effects
The most frequent effects are digestive: nausea, vomiting, diarrhea, constipation, stomach pain, bloating, and reduced appetite. These are most common when starting and after each dose increase, and for many people they ease over weeks. Fatigue, headache, dizziness, and injection-site reactions are also reported. Clinicians manage these with slower titration, smaller meals, avoiding high-fat foods, staying hydrated, and sometimes medication for nausea or constipation. If digestive effects are severe or persistent, that is a reason to contact your clinician, not to push through.
Serious warnings on the labeling
These are drawn from the labeled warnings for the approved products. The specific wording differs by product; read the medication guide that comes with yours.
- Thyroid C-cell tumors. A boxed warning based on rodent studies. The medications are not for people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2.
- Pancreatitis. Severe, persistent abdominal pain, sometimes radiating to the back, with or without vomiting, needs urgent evaluation.
- Gallbladder problems. Gallstones and gallbladder inflammation have been reported, particularly with rapid weight loss.
- Low blood sugar. Mainly a risk for people also taking insulin or sulfonylureas; doses of those may need adjustment.
- Kidney injury. Usually linked to dehydration from vomiting or diarrhea. Fluids matter.
- Severe allergic reactions. Swelling of the face, lips, tongue, or throat, or difficulty breathing, is an emergency.
- Diabetic retinopathy complications. A concern for people with existing diabetic eye disease.
- Suicidal thoughts. Monitoring for mood changes is advised; report new or worsening depression or suicidal thoughts right away.
- Slowed stomach emptying. Relevant for anesthesia; tell any surgeon or anesthesiologist you are on a GLP-1 well before a procedure.
Who should not take these, or needs in-person care first
Online programs are designed for relatively uncomplicated patients. If any of the following apply, an in-person evaluation is the safer starting point, and a careful online program will say so.
- Personal or family history of medullary thyroid cancer or MEN 2.
- History of pancreatitis.
- Pregnant, breastfeeding, or planning pregnancy. These medications are generally stopped well before a planned pregnancy; discuss timing with a clinician.
- Type 1 diabetes, or type 2 diabetes managed with insulin or sulfonylureas, where dose coordination is needed.
- History of an eating disorder.
- Significant kidney or liver disease.
- Severe gastrointestinal disease, including gastroparesis.
- Diabetic retinopathy.
- Under 18 (adolescent use exists for some products but is a specialist decision).
- Active or recent serious depression or suicidal thoughts.
- Known allergy to the medication or its components.
This list is not complete and is not a substitute for the prescribing information. Its purpose is to help you recognize when "a quick online form" is the wrong tool for your situation.
Managing the common effects
Nausea is the effect most likely to make people quit, and it is also the most manageable. Standard advice from clinicians includes eating smaller meals more slowly, stopping when you first feel full, avoiding fried and very fatty foods for the first weeks after each dose change, avoiding lying down right after eating, and keeping bland foods on hand. Some clinicians prescribe anti-nausea medication for the escalation weeks. If nausea is severe or you cannot keep fluids down, that is not something to tough out; it is a reason to contact your clinician and possibly slow the titration.
Constipation responds to fluids, fiber, and movement, and to over-the-counter remedies your clinician can recommend. Diarrhea usually improves with time and dietary adjustment. Reflux and burping are common and often improve with the same small-meal approach. Fatigue in the early weeks is often related to eating much less; make sure you are getting enough calories and protein even when appetite is low.
Interactions to raise with your clinician
Because these medications slow how quickly your stomach empties, they can change how other oral medications are absorbed. This matters most for drugs with narrow dosing windows and for oral contraceptives, where some product labels advise a backup method for a period after starting or increasing the dose. Insulin and sulfonylureas raise low-blood-sugar risk. Blood pressure medication doses sometimes need adjusting as weight falls. Bring a complete list to your visit and ask specifically about each one.
Things that are not on the label but matter
Muscle loss. Rapid weight loss includes lean mass. Adequate protein and resistance training are standard advice and a good program will bring them up without being asked.
Nutrition. Eating much less makes it easy to under-eat protein, fiber, and micronutrients. Some clinicians recommend a basic multivitamin; ask.
Alcohol. Many people find their tolerance and desire for alcohol drop. Combining alcohol with reduced food intake and possible low blood sugar deserves caution.
Stopping. Weight regain after stopping is common in trials. The plan for maintenance, whether that is staying on a lower dose, tapering, or transitioning to lifestyle-only, should be part of the conversation from the start.
When to contact someone
| Situation | Action |
|---|---|
| Mild nausea, constipation, reduced appetite | Message your clinician at the next check-in; use the usual management steps |
| Vomiting or diarrhea lasting more than a day, unable to keep fluids down | Contact your clinician the same day |
| Severe abdominal pain, especially radiating to the back | Seek urgent care or emergency care |
| Swelling of the face or throat, trouble breathing | Emergency services |
| New or worsening depression or thoughts of self-harm | Contact a clinician right away; in the US, call or text 988 for immediate support |
| Lump in the neck, trouble swallowing, hoarseness | Contact your clinician promptly |
Your online clinician is not an emergency service. Telehealth messaging can take hours or days. For anything on the urgent or emergency rows above, use local urgent care or emergency care and inform the program afterward.
How a good program handles all this
It screens for every contraindication on intake and declines or refers when one appears. It explains side effects before you inject. It titrates slowly. It gives you a clear, fast way to report problems, and it tells you plainly when to stop messaging and go to a doctor. If a program treats side effects as an inconvenience rather than clinical information, that is the clearest signal it is selling a product rather than providing care.