Side effects: what to expect, what to flag
Most people on a GLP-1 have side effects, especially in the first few weeks. Most of them are gastrointestinal and most fade. A few are serious enough that you should know what to flag immediately.
Nausea, fullness, constipation, and diarrhea are common and usually transient. Pancreatitis, gallbladder issues, and a specific thyroid warning are uncommon but worth knowing about.
The most common side effect by far is gastrointestinal: nausea, feeling full quickly, occasional vomiting, constipation, or diarrhea. These are most prominent in the first weeks and after each dose increase. Starting at lower doses and titrating up slowly is the standard strategy to reduce them. Most people find the symptoms ease over a few months.
Less common but worth knowing: pancreatitis (severe persistent abdominal pain, especially radiating to the back, with nausea), gallbladder problems (right-upper-abdomen pain, especially after fatty meals), and acute kidney injury usually triggered by dehydration from prolonged vomiting.
There is a boxed warning on this class about a possible risk of medullary thyroid carcinoma based on rodent studies. The drugs are not recommended for people with a personal or family history of medullary thyroid cancer or with Multiple Endocrine Neoplasia syndrome type 2 (MEN2). Whether a similar risk exists in humans is not established, but the warning is part of the label and your doctor should ask about that family history.
Hypoglycemia (low blood sugar) is uncommon with GLP-1s alone, but the risk goes up if you're also on insulin or a sulfonylurea. Doses of those other medications often need to be lowered when a GLP-1 is added.
What this means for you
If you start a GLP-1, expect some GI discomfort and know that it usually settles. Severe abdominal pain, persistent vomiting, or signs of dehydration are not normal — call your doctor. Bring up any personal or family history of thyroid cancer before the first dose, not after.
Which of these side effects would you most want to ask a doctor about before starting one of these medications?