GLP-1 side effects, sorted by what to do about them

Common, and usually manageable

• ◆Nausea — concentrated in the weeks after each dose increase. The standard response is to hold the dose rather than push through.
• ◆Constipation and diarrhoea, often both in sequence. Fibre and fluid help; a bowel that is not moving and not improving is a reason to call.
• ◆Reflux, burping, and early fullness.
• ◆Fatigue during the escalation phase.

Watch closely

• ◆Vomiting. Occasional is common; repeated is not, and it carries the dehydration risk above.
• ◆Loss of lean mass. A meaningful share of the weight lost is not fat. Protein intake and resistance training are the countermeasure, and most subscription services do not mention this at all.
• ◆Hypoglycaemia, particularly alongside insulin or sulfonylureas.
• ◆Injection-site reactions — FDA’s alert on unapproved GLP-1 products describes reports including “redness, site swelling, pain, and a red lump at the injection site.”

The boxed warning

This class carries a boxed warning based on rodent thyroid C-cell tumour data. The medicines are contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2. Any intake that does not ask about this is not screening you properly.

The compounded-specific risk

Compounded products add a failure mode the approved ones do not have: the dose arithmetic moves to you. FDA has published an alert about dosing errors with compounded semaglutide, describing adverse event reports “some requiring hospitalization” that may relate to overdoses. A vial and a syringe, with concentration varying between compounders, is a different proposition from a pre-filled pen.

If you are using a compounded product, get the concentration and your dose written down in the same units, and confirm them before every injection rather than from memory.