Ozempic side effects: What every Australian should know before starting

GLP-1 weight loss medications — Ozempic, Wegovy, Mounjaro, Saxenda and Duromine — are now among the most prescribed medicines in Australia. Nearly 500,000 Australians are currently using them, and with Ozempic supply fully restored, Wegovy now widely available, and Mounjaro approved for both diabetes and weight management, that number is growing every month.

They are also, quite rightly, among the most talked-about medications in the country. And with that comes plenty of questions — particularly about side effects. What should you expect? What is normal, and what is a warning sign? How long do side effects last? And how can you reduce them?

This guide covers everything Australians need to know about GLP-1 medication side effects in 2026 — based on the latest clinical evidence and the real experiences of people taking these medications. Because being informed isn't the same as being scared. It means you know what to expect, when to act, and how to give your medication the best chance of working for you.

How GLP-1 medications work — and why side effects happen

To understand the side effects, it helps to understand the mechanism. Ozempic, Wegovy and Saxenda all mimic a hormone called GLP-1 (glucagon-like peptide-1), which your body naturally produces after eating. GLP-1 signals to your brain that you are full, slows the rate at which your stomach empties, and helps regulate blood sugar levels.

Mounjaro goes one step further, mimicking both GLP-1 and a second hormone called GIP (glucose-dependent insulinotropic polypeptide). This dual action makes it the most potent of the current approved weight loss medications, but also means its side effect profile can be more pronounced, particularly in the early weeks.

Duromine (phentermine) works differently. It is an appetite suppressant that acts on the central nervous system — yet it shares some of the same practical challenges around reduced appetite and digestive changes.

Most Ozempic side effects, particularly the gastrointestinal ones, are a direct result of that slowed gastric emptying. Your stomach is doing something it is not used to, and your body takes time to adjust.

Common side effects of Ozempic, Wegovy and Mounjaro

The most commonly reported side effects of GLP-1 medications are gastrointestinal. According to clinical trial data, nausea affects 15–44% of patients depending on the medication and dose, with the highest rates seen at the start of treatment and at each dose increase.

Gastrointestinal side effects (most common)

• Nausea — the most common side effect; typically peaks in weeks 1–4 at each new dose and gradually improves
• Vomiting — less common than nausea; usually mild and short-lived
• Diarrhoea or constipation — both can occur; staying well hydrated helps significantly
• Bloating and abdominal discomfort — often related to slowed gastric emptying
• Reflux or heartburn — particularly after large meals or eating too quickly

The good news: for the majority of people, these symptoms are mild to moderate and improve significantly after the first 8–12 weeks as the body adapts. They tend to return briefly with each dose increase, then settle again.

Other commonly reported side effects

• Fatigue — particularly in the first few weeks; often related to reduced food intake
• Headaches — usually temporary and linked to dietary changes and lower calorie intake<
• Dizziness — can occur, especially if not eating enough or if dehydrated
• Reduced appetite — technically the intended effect, but can become problematic if it leads to undereating
• Changes to heart rate — a mild increase in resting heart rate has been observed in some patients on semaglutide

Serious side effects: what to watch for

While most side effects are manageable, there are serious conditions that have been reported with GLP-1 medications. These are uncommon, but you should know what to look for.

• Pancreatitis — severe upper abdominal pain that may radiate to the back. Stop medication immediately and seek medical attention.
• Thyroid tumours — GLP-1 medications carry a warning about medullary thyroid carcinoma (MTC), particularly in people with a personal or family history of thyroid cancer. Symptoms include a lump in the neck, difficulty swallowing, or hoarseness.
• Gallbladder problems — rapid weight loss of any kind can increase gallstone risk. Symptoms include upper right abdominal pain, nausea, and fever.
• Kidney concerns — severe vomiting and dehydration on GLP-1 medications has been associated with acute kidney injury in some cases. Staying hydrated is important.
• Vision changes — some cases of a condition called NAION (non-arteritic anterior ischaemic optic neuropathy) have been reported; speak to your doctor if you notice any sudden changes to your vision.
• Cardiovascular risks — GLP-1 medications, particularly semaglutide, are actually associated with reduced cardiovascular events in people with existing heart disease. However, Duromine (phentermine) can increase heart rate and blood pressure and requires careful monitoring.

How long do Ozempic side effects last?

For most people, the most significant side effects of Ozempic and other GLP-1 medications peak in the first 4–12 weeks and then gradually improve. Nausea typically lasts 2–5 days after each injection and becomes less severe as your body adjusts.

Side effects tend to return — usually more mildly — with each dose increase, then settle again. By the time most people reach their target maintenance dose, the side effects have substantially diminished for the majority of patients. Clinical trial data for semaglutide shows that nausea rates drop significantly after week 20, which corresponds to when most patients reach their target dose.

If you are still experiencing significant side effects after 12 weeks at a stable dose, speak to your prescribing doctor. Dose reduction, medication switching, or prescription anti-nausea medications may be appropriate.

How to reduce GLP-1 side effects: practical strategies

The most effective thing you can do to reduce Ozempic and GLP-1 side effects is to change how and what you eat. The medication is doing its job — your job is to support it with the right nutrition.

Eat smaller, more frequent meals

Three large meals a day does not work well on GLP-1 medication. Your stomach is already emptying slowly — adding a large volume of food on top of that is a reliable way to trigger nausea and discomfort. Aim for 4–5 smaller meals across the day, stopping well before you feel full.

Prioritise protein at every meal

This is the most important nutritional principle on GLP-1 medication. When you eat significantly less, protein is the first thing you must protect. Research shows that without adequate protein intake, up to 25–40% of weight lost on GLP-1 medications can come from lean muscle mass rather than fat — which affects your energy, strength and long-term metabolism. Aim for at least 25–35g of protein per meal.

Avoid the foods that make nausea worse

High-fat, fried, very spicy, and heavily processed foods are the most common nausea triggers on GLP-1 medications. Your stomach is already slowed — these foods slow it further and reliably cause discomfort. Alcohol should also be avoided or minimised: it provides empty calories, irritates your stomach, and can cause dangerous blood sugar drops.

Time your injections strategically

Nausea typically peaks 24–48 hours after a weekly injection. If you inject on a Friday evening, expect Saturday and Sunday to be your most challenging days nutritionally. Plan lighter, gentler meals for those days and keep your schedule clear if possible.

Stay hydrated — but not during meals

Dehydration significantly worsens GLP-1 side effects, particularly nausea, headaches and fatigue. Aim for 2 litres of water daily, sipping slowly rather than gulping. Avoid drinking with meals — it can increase the feeling of uncomfortable fullness. Wait 30 minutes before and after eating.

The side effect nobody talks about: muscle loss on GLP-1 medication

Nausea gets all the attention. But the side effect that has the biggest long-term impact on your health outcomes is muscle loss — and it is much less talked about.

When you eat significantly less on GLP-1 medication, your body does not automatically draw all its energy from fat reserves. Without adequate protein, research suggests that between 25–40% of the weight lost on GLP-1 medications can come from lean muscle tissue. Muscle loss affects your metabolism, your strength, your energy levels, and your ability to maintain your weight long term once you reach your goal.

The practical solution is straightforward: prioritise protein at every meal, keep active (resistance training is particularly valuable), and — if your appetite is too low to eat enough protein from scratch — consider a meal solution that does the nutritional planning for you.

When to seek medical help

Most Ozempic and GLP-1 side effects are manageable at home. But these symptoms require prompt medical attention:

• Severe abdominal pain, especially upper abdominal pain radiating to the back — may indicate pancreatitis
• Vomiting multiple times per day or inability to keep fluids down for 24+ hours
• Signs of dehydration: dark urine, extreme thirst, dizziness, or confusion
• Any sudden changes to your vision
• A lump or swelling in your neck, or difficulty swallowing
• Significant mood changes, depression, or any thoughts of self-harm — speak to your doctor immediately
• Nausea that has not improved after 12 weeks at a stable dose

Never hesitate to contact your prescribing GP or a telehealth service if something doesn't feel right. Your doctor can adjust your dose, prescribe anti-nausea medication, or review whether a different medication might suit you better.

Frequently Asked Questions about Ozempic side effects

Is Ozempic safe to take long term?

Based on current evidence, yes — for the right patients and with appropriate medical supervision. Ozempic has been in clinical use since 2017 and has over nine years of real-world safety data globally. The major clinical trials (STEP, LEADER, SELECT) have all demonstrated cardiovascular benefits in addition to weight loss for high-risk patients. As with any medication, ongoing monitoring by your GP is important, particularly for thyroid, kidney and gallbladder health.

Do Ozempic side effects go away?

For the majority of people, yes. Gastrointestinal side effects — nausea, vomiting, diarrhoea — typically peak in the first 4–12 weeks and improve substantially as the body adjusts. They may return briefly at each dose increase but generally become less severe over time. If side effects are still significant after 12 weeks at a stable dose, speak to your prescribing doctor.

What are the most common side effects of Wegovy and Mounjaro?

Wegovy (semaglutide 2.4mg) and Mounjaro (tirzepatide) share a similar side effect profile to Ozempic, with nausea, vomiting, and gastrointestinal discomfort being most common. Because Wegovy is prescribed at a higher dose than Ozempic for weight management, nausea rates can be higher — affecting up to 44% of Wegovy users in clinical trials. Mounjaro's dual mechanism (GLP-1 + GIP) makes it the most potent option but can also mean more pronounced side effects, particularly early on. Both medications use the same gradual dose-escalation approach to minimise this.

Can I take anti-nausea medication with Ozempic?

Yes, in many cases. Your prescribing doctor may recommend over-the-counter options like ginger supplements or vitamin B6, or prescription medications such as ondansetron (Zofran) for more significant nausea. Always discuss with your doctor before taking any additional medications, including over-the-counter options, while on GLP-1 therapy.

Does Ozempic cause hair loss?

Hair loss (medically called telogen effluvium) has been reported by some people on GLP-1 medications. It is generally understood to be a result of rapid weight loss and nutritional deficiency rather than the medication itself. The body responds to significant calorie restriction or nutritional stress by shedding hair. Ensuring adequate protein intake — particularly during active weight loss — is the most effective prevention strategy. For most people, hair loss is temporary and improves once weight stabilises.

I'm having surgery — do I need to stop Ozempic?

You should discuss this with both your prescribing doctor and your anaesthetist before any planned procedure. GLP-1 medications slow gastric emptying, which increases the risk of aspiration (stomach contents entering the lungs) under general anaesthesia. Current guidance varies — some anaesthetists recommend pausing GLP-1 medications for 1–2 weeks before surgery. Do not stop your medication without medical advice, but do inform your surgical team well in advance.

Supporting your GLP-1 journey with the right nutrition

Managing side effects is really about managing nutrition. The medications work — the challenge is giving your body what it needs when your appetite has been significantly reduced. Every meal has to count more when you're eating less.

That is where Dietlicious comes in. Our GLP-1 Support Meals are Australia's only purpose-built meal delivery solution for people on weight loss medications — chef-prepared, high-protein, portion-controlled and delivered frozen across Australia. No cooking required. No meal planning. No guessing whether you're hitting your protein targets.

First written: April 2025

Revised: May 2026

Written by: Joanna O'Sullivan, GDHumNutr

^{Medical Disclaimer
This article is for informational purposes only and does not constitute medical advice. Always consult your prescribing GP, endocrinologist, or healthcare provider before starting, changing, or stopping any weight loss medication. Individual responses to GLP-1 medications vary significantly. If you are experiencing concerning symptoms, seek medical attention promptly.}

Citations & References

Kommu S, Whitfield P. Semaglutide. StatPearls [Internet]. 2025. Available from: https://www.ncbi.nlm.nih.gov/books/NBK603723/

Wharton S, et al. Gastrointestinal tolerability of once-weekly semaglutide 2.4 mg in adults with overweight or obesity. Diabetes Obes Metab. 2022;24(1):94-105.

Shu Y, et al. Gastrointestinal adverse events associated with semaglutide: A pharmacovigilance study based on FDA adverse event reporting system. Front Public Health. 2022;10:996179.

Alhazmi A, le Roux C. Do no harm: managing nausea and vomiting in GLP-1 based obesity therapies. Front Endocrinol. 2026.

Therapeutic Goods Administration (TGA). Updated guidance on GLP-1 receptor agonists. December 2025. Available from: tga.gov.au