What do GLP-1 medicines do?

What does GLP-1 mean?

GLP-1 is short for glucagon-like peptide-1. It's a hormone your gut releases after you eat, telling your body that food has arrived.

It's made mostly in the lower part of your small intestine and in your large intestine.¹ It sends signals to your brain, stomach and pancreas (an organ behind your stomach that makes hormones).

Your body's own GLP-1 doesn't last long. An enzyme (a protein that breaks other things down) clears it in about 1 to 2 minutes.¹ So its natural effect is small and short.

What do GLP-1 medicines do in your body?

A GLP-1 medicine is a lab-made version of GLP-1, changed so your body can't break it down quickly. Your own GLP-1 is gone in 1 to 2 minutes. Semaglutide, the medicine in Wegovy and Ozempic, keeps working for about a week.^1,10

So the "food has arrived" message that your gut normally sends for a few minutes after a meal is sent all day, every day, and more strongly.

In short: the brain and stomach effects are why people eat less and lose weight. The pancreas and liver effects are why these medicines lower blood sugar in type 2 diabetes.

Because the pancreas and liver effects only switch on when sugar is high, the medicine mostly leaves normal sugar levels alone. Sugar can still drop too low if it's taken with insulin or certain other diabetes medicines.¹⁰

Why do people lose weight on them?

Mainly because they eat less. In a small study, semaglutide did not change the calories people burned at rest.⁹

That study gave 30 people semaglutide 1 mg or a dummy injection (one with no medicine in it) for 12 weeks each. On semaglutide, they ate 24% less across a full day of eat-as-much-as-you-like meals.⁹ They also reported less hunger and fewer food cravings.⁹

The two biggest weight trials are called STEP 1 (semaglutide, made by Novo Nordisk) and SURMOUNT-1 (tirzepatide, made by Eli Lilly). Each one worked the same way:

• People were split at random into two groups. One group got the medicine. The other got a dummy injection.
• Both groups got the same diet and exercise advice, and nobody knew which injection they were on.
• So the gap between the two groups is what the medicine itself added.^14,15

Average weight lost. Kilograms are for someone who starts at 90 kg (198 lb).

Which works better? You can't tell by comparing the two cards above, because they were different trials with different people. One trial, SURMOUNT-5, tested the two medicines against each other in the same group of people. Each person took the highest dose they could manage. It was paid for by Eli Lilly, the maker of tirzepatide.¹⁶ Tirzepatide also acts on a second gut hormone, called GIP (glucose-dependent insulinotropic polypeptide), which may help explain the difference.⁴

People with type 2 diabetes usually lose less. STEP 2 ran the same test in people with diabetes: about 9 kg lost instead of 13 kg, on the same dose.^14,17

All of these are averages. Some people lose much more, and some lose very little.¹⁴

Not all the weight lost is fat. A scan study inside STEP 1 looked at 140 people. On semaglutide, fat fell by about 19% and lean mass by about 10%.²⁰ In other words, people lost about a fifth of their fat and about a tenth of their lean mass. Lean mass means everything that isn't fat. It includes muscle, but also organs, bone and water.²¹ Guide 8 covers eating and exercise on these medicines.

Do the results hold for people of different ethnic backgrounds?

Trials in East Asian people show similar weight loss. None of the trials on this page was run specifically in South Asian or Black people.

• Japan and South Korea (401 people, STEP 6): 13.2% of body weight lost on semaglutide 2.4 mg over 68 weeks, against 2.1% on a dummy injection.²²
• China (210 people, SURMOUNT-CN): 13.6% of body weight lost on tirzepatide 10 mg and 17.5% on 15 mg over 52 weeks, against 2.3% on a dummy injection.²³
• Japan (225 people analysed, SURMOUNT-J): people on tirzepatide lost about 16% (10 mg) and 21% (15 mg) more of their body weight than people on a dummy injection, over 72 weeks.²⁴

A study in England found South Asian people at a BMI of about 24 had the same diabetes risk as white people at 30.²⁵ That's why Australian guidance uses lower BMI cut-offs for Asian people, and recommends them for Aboriginal and Torres Strait Islander people.¹² The PBS criteria the PBAC recommended for Wegovy in heart disease use a lower BMI line for the same groups.²⁶ Guide 1 explains these cut-offs. The product information for weight management uses the same BMI numbers for everyone.³¹

How is this different from metformin and other diabetes pills?

GLP-1 medicines lower blood sugar and also reduce appetite. On the PBS they are added to other diabetes medicines, not used first.²⁷

Metformin mainly stops your liver releasing too much sugar and helps your body use insulin better. It doesn't make your pancreas release more insulin.²⁸ On the PBS, the usual path starts with metformin. A GLP-1 medicine is subsidised only when an SGLT2 inhibitor (a tablet that makes you pass extra sugar in your urine) didn't work well enough, couldn't be used or wasn't tolerated, and HbA1c is still above 7% on metformin, a sulfonylurea or insulin. A GLP-1 isn't subsidised together with an SGLT2 inhibitor for diabetes, unless the SGLT2 inhibitor is for heart failure or kidney disease.²⁷

HbA1c is a blood test showing your average sugar over the past few months. In a 30-week trial of Ozempic on its own, HbA1c started around 8.1% (65 mmol/mol). It fell by 1.4 to 1.6 percentage points, against 0.1 on a dummy injection.²⁹ That means from about 8.1% to about 6.5–6.7%.

The type 2 diabetes path covers this in more detail: I have type 2 diabetes.

Who these are for, and who they're not for

In Australia, the TGA approves each brand for set uses: type 2 diabetes, weight management, or both. Whether one suits you is a decision for you and a doctor.

• Type 2 diabetes: Ozempic, Rybelsus, Trulicity and Mounjaro.^2,3,4,8
• Weight management: Wegovy and Mounjaro.^4,31
• Teenagers: Wegovy is approved from age 12 for young people with obesity who weigh over 60 kg (132 lb), alongside diet and activity. It should be stopped if their BMI hasn't fallen by at least 5% after 12 weeks on the full or highest tolerated dose. Mounjaro is approved for type 2 diabetes from age 10 in children weighing 50 kg (110 lb) or more.^4,31
• Heart protection: since December 2024, Wegovy is approved to lower the risk of heart attack and stroke in adults with heart or blood-vessel disease, a BMI of 27 or more and no diabetes.^31,32
• Kidney disease in type 2 diabetes: Ozempic is approved to lower the risk of kidney decline and heart-related death in adults with both.²
• Sleep apnoea: Mounjaro is approved for moderate to severe obstructive sleep apnoea in adults with obesity.^4,33
• Fatty liver with scarring (MASH): Wegovy is approved for adults with moderate to advanced liver scarring, through the TGA's provisional pathway, which means more evidence is still to come.³¹

The rules for weight in the product information are a BMI of 30 or more, or 27 to 30 with at least one weight-related condition such as high blood pressure.^4,31 No GLP-1 medicine is subsidised on the PBS for weight.⁴² These are points to start a conversation with a doctor, not a sign that you qualify.

Not studied in type 1 diabetes. The Australian Wegovy product information says it hasn't been studied in type 1 diabetes and isn't recommended for it.³¹ (The product information, or PI, is the official prescribing document for a medicine in Australia. Its shorter version for patients is the CMI.)

Tirzepatide and the contraceptive pill. Tirzepatide (Mounjaro) can make the pill work less well. Its product information says to switch to a non-pill method, or add a barrier method such as condoms, for 4 weeks after starting and for 4 weeks after each dose increase.⁴

They're not for losing a few kilos before a holiday or event. Their approved uses start at a BMI of 27 with a weight-related condition.³¹ They're long-term treatments, and weight tends to come back after stopping.^19,35 If that's you, read I want to lose a few kilos.

Who shouldn't take them, and what to ask, is in Guide 4: Should I consider a GLP-1?

Which GLP-1 medicines are approved in Australia?

Every GLP-1 medicine has two kinds of name: the name of the medicine itself, and the brand names it's sold under. Knowing the difference stops a lot of confusion.

GLP-1 medicines work the same way. Semaglutide is the medicine, and Wegovy, Ozempic and Rybelsus are brands of it. Two brands of the same medicine can still differ in dose, in whether they're an injection or a tablet, and in what they're approved for.

A generic is a copy made by another company once the patent ends. In Australia, liraglutide is the only one of these medicines with generic versions, first approved in 2025.⁶ We found no generic semaglutide here.

The GLP-1 medicines approved in Australia, and their brands

Names only, not a recommendation, and not a list of what's right for you. Who pays and how to get them are in Guide 6.

Is Ozempic the same as Wegovy?

Same medicine, different brand. Both are semaglutide, made by Novo Nordisk. They are approved for different uses and go up to different doses.

• Ozempic is approved in Australia for type 2 diabetes, including kidney disease in type 2 diabetes. Weight loss is not one of its approved uses. Its highest dose is 2 mg a week.²
• Wegovy is approved for weight management. Its usual full dose is 2.4 mg a week, and 7.2 mg is allowed for adults who started with a BMI of 30 or more.³¹

Using a medicine for something it isn't approved for is called "off-label". In Australia a doctor may prescribe off-label on their own judgement, but it is scrutinised: Ahpra, which regulates health practitioners, said in September 2026 it may look into doctors with high prescribing rates even without a complaint.⁴⁵ Companies can't promote it: the TGA says it is illegal to advertise Ozempic for weight loss, even to health professionals.³⁸ During the Ozempic shortage, from 2022 until July 2025, doctors were asked not to start new patients on it, so that people with diabetes could get it.^40,44 Wegovy is the semaglutide brand approved for weight.³¹

Mounjaro is a different medicine: tirzepatide, made by Eli Lilly.⁴

How long do they take to work, and how long do they last?

You start on a low dose and go up slowly, usually every 4 weeks. Weight loss builds over many months.^14,31

In trials, stomach side effects happened mostly while the dose was still going up.^15,16

1. Weeks 1–40.25 mg once a week
2. Weeks 5–80.5 mg
3. Weeks 9–121 mg
4. Weeks 13–161.7 mg
5. Week 17 on2.4 mg, the usual full dose
6. If needed7.2 mg (given as 3 injections of 2.4 mg), for adults who started with a BMI of 30 or more, after at least 4 weeks on 2.4 mg

In STEP 1, average weight kept falling until about week 60, then levelled off.¹⁴ The Australian product information has no adult stopping rule based on weight; the 5% check after 12 weeks applies to teenagers.³¹ The Australian algorithm sets weight-loss targets of 10–15% for many people, and says to change the plan if targets aren't reached.¹²

Why once a week, and how long it stays in your body

Your body clears semaglutide slowly. About half of each dose is gone after a week, so one injection a week keeps enough in your blood.^1,10

The same slow clearing means the medicine doesn't leave your body the day you stop taking it. After your last dose, it takes about 5 weeks to leave your blood.²⁹

This matters most if you're planning a pregnancy. The Australian product information says to stop semaglutide at least 2 months before a planned pregnancy, because of how slowly it leaves the body.³¹

Do they do anything besides weight and sugar?

In one large trial, semaglutide lowered the combined risk of heart attack, stroke and heart-related death. Most of that came from fewer heart attacks.

The SELECT trial followed 17,604 people for about 3 years.⁴¹ All were 45 or older, had overweight or obesity, and no diabetes. All already had heart or blood-vessel disease: a past heart attack, a past stroke, or narrowed leg arteries.¹⁰

That's about 1 fewer event for every 67 people treated. Heart attacks fell from 3.8 to 2.8 in 100. Strokes went from 2.0 to 1.8 in 100, a difference too small to be sure of.¹⁰

The TGA registered Wegovy for this use in December 2024.³² In November 2025 the PBAC, which advises the government on PBS subsidies, recommended subsidising it for people who have already had a heart attack, stroke or similar event and have a BMI of 35 or more (32.5 for Asian, Aboriginal or Torres Strait Islander people).²⁶ As of July 2026 it had not been listed on the PBS.⁴² It applies to people who already have that disease, not to everyone.

Other approved uses beyond weight and sugar: kidney disease in type 2 diabetes (Ozempic), sleep apnoea with obesity (Mounjaro) and, provisionally, fatty liver with scarring (Wegovy).^2,4,31

What these medicines do not do

Are these medicines new?

No. The first GLP-1 medicine was approved in the US in 2005. What's new is how strong and long-lasting they've become, and that some now come as tablets.^3,43

The first one, exenatide, came from a substance found in the saliva of a lizard, the Gila monster.¹ Later versions were changed to last longer in the body. Half of each semaglutide dose is cleared in about a week.^1,10

1. 2005Exenatide (Byetta) approved in the US⁴³
2. Aug 2019Ozempic approved in Australia for type 2 diabetes³⁶
3. Feb 2022Rybelsus tablets approved for type 2 diabetes³
4. Sep 2022Wegovy approved for weight management³⁷
5. Dec 2022Mounjaro approved for type 2 diabetes⁴⁶
6. Aug 2024Wegovy goes on sale, almost two years after approval⁴⁴
7. Sep 2024Mounjaro approved for weight management³⁴
8. Oct 2024Pharmacy-made (compounded) GLP-1s banned¹¹
9. Dec 2024Wegovy approved for heart protection³²
10. Jun 2025Mounjaro approved for sleep apnoea³³
11. Jul 2025Ozempic shortage ends⁴⁰
12. Dec 2025Saxenda no longer sold⁵

Questions people ask