A Rundown of GLP-1 Side Effects Patients Should Know

GLP-1 receptor agonists such as semaglutide — sold as Ozempic and Wegovy — are prescribed for type 2 diabetes and weight loss, and their benefits are widely reported. But the side effects that patients experience, and the ones that generate the most conversation, range from everyday digestive discomfort to rare conditions that can affect vision or complicate surgery.

Nausea, vomiting and diarrhoea are the most commonly reported adverse effects and have been present in clinical data since the drugs were first approved for diabetes. Beyond the gut, endocrinologists have observed that patients can lose lean muscle as they lose weight, with some studies suggesting higher protein intake may help reduce that loss. Patients have also described dry mouth, tooth sensitivity and gum inflammation — sometimes called 'Ozempic teeth' — which experts link to dehydration caused by the drugs.

Less common but more serious concerns include a rare form of eye damage known as non-arteritic anterior ischemic optic neuropathy, or NAION, which the European Medicines Agency said could affect up to one in 10,000 people taking semaglutide. The US Food and Drug Administration added a warning in 2024 about pulmonary aspiration during general anaesthesia or deep sedation, and most GLP-1 drugs carry a boxed warning about thyroid C-cell tumours. More recent reports describe hair loss, emotional flattening and interference with certain cancer scans, though the evidence for several of these remains less settled.

Which GLP-1 Risks Are Well Established and Which Are Still Emerging

Gastrointestinal and Muscle Effects Have the Strongest Evidence

Nausea, vomiting and diarrhoea are not surprising because GLP-1 drugs slow stomach emptying and affect gut signalling. These effects have been documented consistently since initial FDA approvals, which makes them among the most reliable side-effect information available to patients and clinicians. Muscle loss is also well recognised by endocrinologists as a consequence of rapid weight reduction, though the degree varies and higher protein intake is a commonly discussed mitigation rather than a proven fix.

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Rare Eye and Thyroid Risks Require Context

The European Medicines Agency's warning on NAION places the risk at roughly one in 10,000 people, so it is rare but potentially severe. The mechanism is reduced blood flow to the optic nerve head. For thyroid C-cell tumours, the class has long carried a boxed warning, but newer research suggests the apparent increased risk may partly reflect more intensive surveillance of patients taking these drugs rather than a direct causal jump. Both points matter for patients weighing the drugs' benefits against a low-probability harm.

The Anesthesia Guidance Shows How Quickly Evidence Is Evolving

When the FDA added a warning on pulmonary aspiration during surgery, anesthesiologists initially advised stopping GLP-1 drugs beforehand. That position has since softened: the American Society of Anesthesiologists now says most patients can continue taking the drugs until the day of surgery. This shift illustrates that many GLP-1 side effects are still being characterised, and that guidance for clinicians and patients can change as postmarketing data accumulate.

Questions Patients on GLP-1 Drugs Should Raise With Their Clinicians

  • If you are scheduled for surgery or a procedure involving sedation, tell the anaesthesia team you take a GLP-1 drug; current American Society of Anesthesiologists guidance says most patients can continue until the day of surgery, but individual plans may differ.
  • Seek prompt eye care if you notice sudden vision loss or other visual changes while taking semaglutide, because NAION — though rare at roughly one in 10,000 — requires urgent attention.
  • If you develop persistent dry mouth, tooth sensitivity or gum inflammation, discuss dehydration-related oral effects with your prescriber or dentist rather than stopping the medication on your own.
  • Ask your prescriber about the boxed warning for thyroid C-cell tumours before starting or continuing a GLP-1 drug, particularly if you have a personal or family history of thyroid tumours.
  • If you are concerned about losing muscle while losing weight, raise the question of protein intake with your clinician; studies suggest higher protein may help offset some lean mass loss, but it is not a guaranteed fix.