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Tried diet after diet? What to know about GLP-1 medicines
Everyone seems to be talking about weight-loss injections. Here is what these prescription medicines really do, who they are meant for, the side effects, and what happens when you stop.
You know how it goes.
You cut down on rice. You switch to kopi-o kosong. You walk after dinner. For a few weeks, maybe a few months, it works. The scale moves, and your clothes feel looser.
Then life happens. A busy month at work. Office makan every Friday. Chinese New Year, and the goodies that sit on the table for weeks. Slowly, the weight comes back.
And now, at lunch, your colleagues are talking about weight-loss injections. Someone's cousin is on them. Your phone keeps showing you videos about it. You start to wonder: is this what I have been missing?
It is a fair question. This page gives you straight answers, including the parts that people talk about less.
This is general health information, not medical advice and not an offer of treatment. These medicines are prescription-only in Singapore. They are not suitable for everyone, and whether any treatment is appropriate for you can only be decided by a doctor who has assessed you.
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Why is losing weight so hard to keep up?
Partly because hunger and fullness are not only about willpower. Your hormones shape them too.
If the weight keeps coming back, you may blame yourself. Not enough discipline. Not enough willpower. But that is not how doctors see it. Obesity is described as a long-term condition. It is not a sign of weak character.
One of those hormones is made in your gut, after you eat. It is called GLP-1, and it is the hormone these medicines are built around.
What are GLP-1 medicines?
GLP-1 stands for glucagon-like peptide-1. Your gut releases it after a meal. It does three things. It helps you feel full. It slows down how fast your stomach empties. And it tells your pancreas to release insulin when your blood sugar rises.
GLP-1 receptor agonists are medicines that copy that hormone. They were first made for type 2 diabetes. Some were later registered to treat obesity too. A newer group works on a second gut hormone, called GIP, as well as GLP-1.
For weight management, they are given as an injection under the skin, either once a week or once a day. A tablet form of semaglutide also exists. In Singapore, though, it is registered for type 2 diabetes only, not for weight loss. The active ingredients registered here include liraglutide, semaglutide and tirzepatide.
All of them are prescription-only medicines. That is a legal rule. They can only be supplied on a doctor's prescription, after a consultation, because whether to use them depends on a doctor assessing you as a person.
What do these medicines actually do?
People often describe it simply. You feel full sooner. You stay full for longer. You think about food less.
So you eat less, and it comes from that change in appetite rather than from willpower. The slower emptying of your stomach plays a part too. That is also why the common side effects are in the gut.
Most are injected into the fat just under the skin of your tummy, thigh or upper arm. A pen-style injector is used, with a very short, fine needle, not a normal syringe. Patients are shown how to use the pen before they start.
One thing to be clear about: the effect lasts only while you take the medicine. These medicines treat the condition. They do not cure it.
Who are they meant for?
Not everyone who wants to lose a few kilos. In Singapore, weight is judged against Asian BMI cut-offs. These are lower than the international ones, because health risks start to rise at a lower BMI in Asian people.
A BMI of 23 to 27.4 counts as moderate risk, and 27.5 or above as high risk.
Medicine is kept for a smaller group. The Ministry of Health's clinical practice guidelines on obesity say weight-loss medicines may be considered for adults with:
- a BMI of 30 or above, or
- a BMI of 27.5 to 29.9 together with a weight-related condition, such as high blood pressure, type 2 diabetes or high cholesterol.
The product information registered in Singapore for these medicines uses similar thresholds: a BMI of 30 or above, or 27 or above with at least one weight-related condition, such as high blood pressure, high cholesterol, obstructive sleep apnoea, heart disease, prediabetes or type 2 diabetes.
In every case, the medicine is used together with eating fewer calories and moving more. It is not a replacement for them.
And meeting a number does not mean a medicine is right for you. That depends on your overall health, your other medicines, what you have already tried and the risks below. Only a doctor who has assessed you can make that call.
Do they work for everyone?
In randomised clinical trials, adults with obesity who took these medicines, along with diet and activity changes, lost a lot more weight on average than people given a dummy injection with the same advice. Trials of some of these medicines also reported improvements in blood sugar control and blood pressure. One large trial, in people who already had heart and blood vessel disease, reported fewer cardiovascular events.
But an average is not a promise. The trials cannot tell you what will happen to you. Results vary a lot from person to person. Some people respond very little. Some cannot put up with the side effects.
It is also worth knowing that people in the trials had structured support with diet and activity the whole way through. That is part of why they did well.
Are there other options?
Yes. Medicine is one part of treating obesity, not the whole of it. The recognised options are:
- Diet, physical activity and sleep. The base of every approach, including treatment with medicine. This is the part that decides whether any progress lasts.
- Treating conditions that add to weight gain, and reviewing medicines that can cause it, such as some treatments for diabetes, mood disorders and epilepsy.
- Prescription medicines. Besides the GLP-1 group, other classes are registered in Singapore, including appetite suppressants and medicines that reduce how much fat you absorb. They differ in how they are taken, their side effects and who they suit.
- Bariatric and metabolic surgery, for selected patients, usually where obesity is severe or where medical treatment has not done enough.
Which of these suits you, if any, depends on your BMI, the conditions you have, what you have already tried, and what you prefer after talking it through with your doctor.
What are the side effects?
The common ones are in the gut: nausea, vomiting, diarrhoea, constipation, indigestion and tummy discomfort. They are usually worst when you start, or when the dose goes up, and they often settle. That is why the dose is normally raised slowly.
Less common, but more serious, risks include:
- inflammation of the pancreas (pancreatitis)
- gallstones and gallbladder disease
- dehydration and kidney problems after vomiting or diarrhoea that does not stop
- low blood sugar, when the medicine is combined with certain diabetes treatments
Some people lose muscle as well as fat. That is one reason eating enough protein and staying active matter during treatment.
Because these medicines slow how fast your stomach empties, food can stay in your stomach for longer than usual. Before any procedure that needs sedation or a general anaesthetic, tell the doctor or dentist in charge. There is a risk of stomach contents getting into the lungs.
If you have diabetic eye disease, a quick improvement in blood sugar can make the eye condition worse for a while, so eye checks may be needed.
Know when to get help fast. Severe tummy pain that does not go away, especially with vomiting, needs prompt medical assessment.
Who should not take them?
- People who are pregnant, breastfeeding or planning a pregnancy.
- People with a personal or family history of medullary thyroid carcinoma, or with multiple endocrine neoplasia syndrome type 2.
They are used with caution, if at all, in people who have had pancreatitis. The same goes for some other conditions, including serious kidney or liver disease, diabetic eye disease and some eating disorders, where the risks may outweigh the benefits.
This is not a full list, and the cautions differ between medicines. A doctor checks for these before prescribing, and checks again as treatment goes on.
What happens if I stop?
When treatment stops, appetite usually goes back to what it was, and weight often comes back, sometimes most of it. It is the question many people forget to ask.
That is expected. It does not mean the treatment failed, or that you did. It is the reason obesity is called a long-term condition. If you are thinking about these medicines, talk to your doctor about what happens afterwards, and how long you might use them.
Can I just buy them online?
No. In Singapore these medicines cannot lawfully be sold to the public without a prescription, and the Health Sciences Authority has acted against unauthorised online sales. It can be tempting, especially when friends share links.
Products from unlicensed sellers, or compounded versions, may have the wrong dose, a different substance, or nothing active at all. They also come without the check-ups and monitoring that make treatment safe. If you are thinking about treatment, see a doctor.
Questions worth asking a doctor
If you are reading this for yourself, the useful next step is a conversation with a doctor who can assess you. It helps to go in with questions like these, and a list of the medicines you take now.
- Based on my BMI and health, which options apply to me?
- Is there anything about my eating, activity or sleep we should look at first?
- Could any of my current medicines be adding to my weight?
- What side effects should I watch for, and when should I get help?
- How long would I be on treatment, and what happens when I stop?
Sources: Ministry of Health Clinical Practice Guidelines: Obesity (2016), summarised in Singapore Medical Journal 2016;57(6):292-300; Health Promotion Board, BMI and health risk (HealthHub); product information for medicines registered by the Health Sciences Authority, as published in the National Drug Formulary.
Written for patients in Singapore. General health information only: it is not medical advice, not a recommendation for any particular medicine, and not an offer or promotion of any treatment or product. No brand of medicine is recommended or supplied on the basis of this page. Prescription medicines are supplied only on a doctor's prescription following a consultation.
Medically reviewed by Dr Lim Jia Yang, 15 October 2026.