Most side effects of GLP-1 medication are unpleasant rather than dangerous, and the previous articles in this cluster deal with those. This one is about the short list that is neither: the symptoms the product information itself tells patients to act on, and how quickly. It is worth reading once, early, so you recognise something if it happens rather than looking it up at the time.

Medication Guide: the patient-facing section of the US prescribing information. The wording below is drawn from it. Singapore's registered product information does not publish an equivalent section publicly, so the medicine supplied to you comes with its own patient leaflet — read that too, and follow your doctor's instructions over anything here.

Stop and seek help right away

Severe abdominal pain that will not go away. This is the clearest instruction in the whole document. The Medication Guide for both medicines says: stop using the medicine and call your healthcare provider right away if you have severe pain in your stomach area that will not go away, with or without nausea and vomiting — and notes the pain may be felt from the abdomen through to the back (semaglutide, tirzepatide). That pattern is the labelled warning sign for pancreatitis.

Signs of a serious allergic reaction. Swelling of the face, lips, tongue or throat; severe rash or itching; a very rapid heartbeat; problems breathing or swallowing; fainting or dizziness. The instruction is to stop the medicine and get medical help right away (Medication Guides).

Both of those are "right away" instructions in the source document, not "mention it at your next appointment".

Contact your doctor promptly

Gallbladder symptoms. Pain in the upper abdomen, yellowing of the skin or eyes, fever, or clay-coloured stools (prescribing information). Gallbladder disease is a listed warning for both medicines.

Vomiting or diarrhoea that does not settle. This one is easy to underestimate because it starts as an ordinary side effect. The Medication Guides are explicit that diarrhoea, nausea and vomiting may cause a loss of fluids, which may cause kidney problems, and instruct patients to tell a healthcare provider right away if these do not go away (Medication Guides). Persistence is what the instruction turns on — but severe symptoms on any single day are also a reason to seek advice rather than wait.

Symptoms of low blood sugar, particularly for anyone also taking insulin or a sulfonylurea, in whom the risk is higher. Dizziness or light-headedness, sweating, shakiness, blurred vision, slurred speech, weakness, hunger, headache, irritability, confusion or drowsiness, a fast heartbeat, feeling jittery (Medication Guides).

Vision changes, for anyone with type 2 diabetes. The Medication Guides instruct telling your healthcare provider about changes in vision during treatment, and frame that instruction specifically for patients with type 2 diabetes (Medication Guides). Any sudden change in vision is worth reporting regardless.

A lump in the neck, difficulty swallowing, shortness of breath, or persistent hoarseness. These are the symptoms patients are counselled to report in connection with the thyroid warning (Medication Guides). The underlying evidence is a rodent finding whose human relevance the US prescribing information says has not been determined — this is a report-it item, not a reason for alarm.

Before any procedure

Tell any surgeon, anaesthetist, dentist or endoscopist that you take GLP-1 medication, and do it before the day.

The reason is that these medicines slow stomach emptying, and there have been reports of stomach contents remaining despite normal fasting. Guidance here changed recently and it is worth knowing which version is current: 2023 advice to withhold weekly GLP-1 medication for a week before a procedure was superseded in October 2024 by multi-society guidance stating that most patients should continue taking the medicine before elective surgery, with those at highest risk of gastrointestinal effects advised a 24-hour liquid diet beforehand or other measures (multi-society guidance 2024). Highest risk is identified as being in the dose-escalation phase, having active gastrointestinal symptoms, or being on a higher dose.

So the instruction is not "stop before surgery". It is "tell them, early, so the team can decide". Do not stop a prescribed medicine on your own for a procedure.

What is not on this list

Two things worth saying plainly, because both circulate.

Suicidal thoughts are not a current label warning. This was investigated as a safety signal in 2023. It was removed from both medicines' US product information in February 2026, and it does not appear in the European product information (label change logs). If you encounter a site presenting it as an active warning, that site is out of date. Any change in mood is still worth telling your doctor about — that is true of any medicine, and of weight loss generally.

Ordinary nausea, constipation and reflux are not red flags. They are common, they cluster around dose increases, and they are covered in managing nausea and constipation and reflux. The distinction that matters is persistence and severity, not presence.

The practical version

Keep it simple enough to remember:

  • Severe abdominal pain that will not go away, or signs of an allergic reaction — stop, seek help now.
  • Jaundice, fever, clay-coloured stools, upper abdominal pain — contact your doctor promptly.
  • Vomiting or diarrhoea that will not settle — contact your doctor; this is a dehydration and kidney issue.
  • Any procedure with sedation or anaesthesia — tell the team in advance.
  • Anything that worries you — that is what the consultation is for.

These medicines are Prescription Only in Singapore (HSA register), and the doctor who prescribed yours is the right person to call. In an emergency, go to a hospital emergency department rather than waiting for a clinic appointment.

Individual circumstances vary, and this article is not a substitute for the product information supplied with your medicine or for your doctor's instructions.

This page covers the rest of the body. For the skin at the injection site specifically — a mark that is spreading, increasing pain, warmth or pus — see bruises, marks and lumps, which sets the short list against what is ordinary.

Common questions

When should you stop GLP-1 medication and call a doctor?

The clearest instruction is for severe abdominal pain that will not go away, with or without nausea and vomiting, sometimes felt through to the back — stop and contact a healthcare provider right away (prescribing information). Signs of a serious allergic reaction carry the same urgency.

What are the signs of pancreatitis on GLP-1?

Severe, persistent abdominal pain that may radiate to the back, with or without nausea and vomiting. The product information instructs stopping the medicine and seeking medical attention right away (semaglutide, tirzepatide).

What are the signs of a gallbladder problem?

Pain in the upper abdomen, yellowing of the skin or eyes, fever, or clay-coloured stools — contact a healthcare provider (prescribing information).

When is vomiting or diarrhoea serious?

When it does not go away. Fluid loss can cause kidney problems, and patients are instructed to report persistent nausea, vomiting or diarrhoea right away (prescribing information).

Should I tell my surgeon or dentist I take GLP-1 medication?

Yes, in advance of any procedure involving sedation or general anaesthesia. Current multi-society guidance is that most patients should continue the medicine, with a 24-hour liquid diet or other measures for those at highest risk (2024 guidance) — but the team can only make that judgement if they know.