Side Effects of GLP-1 Receptor Agonists: What to Expect in Weight Management

GLP-1 receptor agonists are increasingly used as part of medical weight management in Australia. Like all prescription medicines, they can cause side effects- but for most people, thankfully these tend to be mild, temporary, and manageable.

Understanding what’s common and what’s rare can help you make an informed decision and know when to seek medical advice.

This guide summarises current evidence, and the key points regarding side effects which are usually outlined to patients by their healthcare providers.

Common side effects (usually mild and temporary)

The most common side effects of GLP-1 receptor agonists involve the gastrointestinal system (stomach and gut). This is not surprising, as these medicines act on gut hormones involved in appetite and digestion.

Common effects include:

Nausea
Vomiting OR diarrhoea
Abdominal discomfort
Bloating
Indigestion
Reflux or a feeling of fullness

Other reported side effects include fatigue, light-headedness, headaches, mood changes and irritation at injection sites.

For most people, these symptoms:

Are mild to moderate
Occur early in treatment
Often improve over time as the body adjusts

Starting at a low dose and increasing gradually (which is the standard medical approach) reduces the likelihood and severity of these effects. Adjustments to diet, and other lifestyle changes may also help (for example eating more fibre if you get constipation).

Less common but more serious side effects

Serious side effects are uncommon, but it’s important to be aware of them.

These may include:

Pancreatitis (inflammation of the pancreas), which can cause severe, persistent upper abdominal pain. This affected less than 1% of patients in most major trials, though may be more likely in people taking the medication longer term. In some studies there was no clear increase in risk.
Significant delayed stomach emptying, leading to ongoing vomiting or inability to tolerate food

Certain people should not use GLP-1 receptor agonists, including those with:

A personal or family history of medullary thyroid cancer
Multiple endocrine neoplasia type 2 (MEN2)

This is why a proper medical history and doctor-led assessment are essential before starting treatment.

Vision-related concerns

There was also a possible concern raised about an increased risk of rare eye conditions but:

Causality has not been established
The absolute risk appears very low if present
Further research is ongoing in this area

Overall, regulatory bodies continue to regard GLP-1 receptor agonists as having a favourable safety profile when prescribed in the correct circumstances and monitored correctly.

Long-term consideration: weight regain after stopping

One important issue to understand is what happens after treatment is stopped.

A large 2026 BMJ systematic review found that:

Weight regain is common after discontinuing GLP-1–based weight management medicines
For newer incretin-based therapies, average regain was approximately 0.8 kg per month
Without ongoing strategies, weight may gradually return toward baseline over 1–2 years

This doesn’t mean treatment “fails” but reflects the reality that obesity is a chronic, relapsing condition, and appetite-regulating biology tends to revert once medication is withdrawn, particularly if not part of a holistic lifestyle plan.

For this reason, GLP-1 medicines work best when used as part of a longer-term, medically guided plan, rather than a short-term fix.

Managing side effects with medical support

Side effects and responses vary from person to person. Discussing potential risks upfront and having access to follow-up care can make a significant difference.

Doctor-led care allows for:

Individualised dose adjustments
Monitoring of symptoms
Early identification of side effects
Planning for longer-term weight maintenance

At Doctors for Weight Loss (powered by Qoctor), consultations are provided by AHPRA-registered Australian doctors via telehealth, with monitoring and follow-up tailored to each patient’s needs.

Quick checklist: when to seek medical advice

Are digestive symptoms or nausea persistent or worsening?
Are you experiencing severe or ongoing abdominal pain?
Are you unable to keep food or fluids down?
Have you discussed a plan for maintaining weight if treatment changes or stops?

If in doubt, seek medical advice from your doctor promptly.

Key takeaway

GLP-1 receptor agonists can be an effective part of weight management for some people. Most side effects are mild and temporary, serious risks are rare, and several early concerns appear less common than once feared.

Understanding side effects — and planning for long-term care — helps ensure these medicines are used safely and realistically.

Data last reviewed: 27 January 2026