GLP-1 injections for weight loss: what to know before you start, and while you're on them

Hardly a week goes by now without someone asking me about "the weight-loss injection". A cousin lost 12 kg before a wedding. A colleague is ordering pens from someone on Instagram. A relative in the UK swears by it.

So let's talk about it properly. What these medicines are, what they can and can't do, and the part that rarely gets mentioned: what you eat while you're on them matters a lot.

One thing first. I'm a dietitian, not your prescribing doctor. Whether a GLP-1 medicine is right for you is a decision for you and your doctor. My job is to help you get the best result from it, and to stay healthy while you do.

What are GLP-1 medicines?

GLP-1 is a hormone your gut releases after you eat. It tells your brain you're full, slows down how quickly your stomach empties, and helps your body release insulin when blood sugar rises.

GLP-1 medicines copy that hormone, but they last much longer. The ones you'll hear about most are:

• Semaglutide, sold as Ozempic (for type 2 diabetes), Wegovy (for weight) and Rybelsus (a tablet)
• Liraglutide, sold as Victoza and Saxenda, an older daily injection
• Tirzepatide, sold as Mounjaro and Zepbound, which acts on GLP-1 and a second hormone, GIP

Most are weekly injections. People on them usually describe the same thing: the constant "food noise" goes quiet, they feel full sooner, and they simply want less.

How well do they work?

Better than anything we've had before. In the large trials, people on semaglutide at the weight-loss dose lost around 15% of their body weight on average over about a year and a half. With tirzepatide at the highest dose, the average was closer to 20%.

Those are averages, though. Some people lose much more, some lose very little. And everyone in those trials was also getting diet and activity support, which is easy to forget.

Who are they for?

Generally, they're prescribed for adults living with obesity, or for people who are overweight and also have a weight-related condition like type 2 diabetes, high blood pressure, sleep apnoea or fatty liver. South Asians tend to develop these problems at a lower weight, which is why doctors often use lower BMI cut-offs for us.

They're not for someone who wants to drop a few kilos for a wedding. And they're not safe for everyone. They aren't used in pregnancy or while trying to conceive, and they're not suitable for people with a personal or family history of certain thyroid cancers, or a history of pancreatitis. That's exactly why a doctor needs to be involved.

Please don't buy these without a prescription

This is the part that worries me most. Pens are being sold through social media, WhatsApp groups and some pharmacies with no prescription and no questions asked. Some are genuine. Some are not. Health authorities around the world, including the WHO, have warned about fake semaglutide pens, and some contained the wrong medicine or the wrong dose.

Even a genuine pen needs to be started at a low dose and increased slowly. Jumping straight to a high dose is a quick way to end up vomiting for days. If you're going to use one of these medicines, get it prescribed, and get it from a pharmacy you trust.

The side effects nobody puts on Instagram

The most common ones are gut-related: nausea, vomiting, bloating, constipation or diarrhoea, and burping. They're usually worst in the first few weeks and after each dose increase, and they often settle.

Less common, but important, are gallbladder problems and pancreatitis. Severe stomach pain that goes through to your back, or vomiting you can't stop, needs a doctor straight away.

If you're also on insulin or tablets like gliclazide or glimepiride, your blood sugar can drop too low as you start eating less. Your doctor may need to adjust those doses.

The muscle problem

Here's what I spend most of my time on with people using these medicines.

When you lose weight quickly, not all of it is fat. A meaningful part can be muscle, and that matters. Muscle keeps your metabolism up, keeps you strong as you age, and helps control blood sugar. Losing a lot of it is how people end up lighter but weaker, and more likely to regain the weight as fat.

You can protect it, mostly with two things: enough protein, and strength exercise.

How to eat on a GLP-1 medicine

Protein first, at every meal. When your appetite is small, every bite counts. Start the meal with the protein: eggs, daal, chana, dahi, chicken, fish, qeema, paneer. If you can only manage half your plate, make sure it's that half.

Small meals, eaten slowly. Your stomach is emptying more slowly than before. Big portions and eating fast are what bring on the nausea. Stop at the first sign of fullness, even if there's food left on the plate.

Go easy on oily and fried food. Rich salans, parathas, pakoras and biryani at dawats are the foods people most often say make them feel sick on these medicines. Lighter cooking makes a real difference.

Don't stop eating altogether. Some people barely eat at all, and it can feel like the medicine is "working". It isn't working in your favour. Skipping meals for days leads to dizziness, weakness, hair fall and more muscle loss.

Drink enough water. Thirst signals get quieter too, and vomiting or diarrhoea can dehydrate you quickly, which is hard on your kidneys. Keep a bottle with you and sip through the day.

Fibre for constipation. Sabzi, fruit, daal, oats and isabgol, along with enough water, help keep things moving.

Lift something. Two or three short strength sessions a week, at home is fine: squats, wall push-ups, lifting water bottles. This is your best protection against losing muscle.

A note on fasting

If you plan to fast in Ramadan, or fast regularly for other reasons, speak to your doctor before you do. A GLP-1 medicine plus long hours without water can dehydrate you quickly, especially in the first weeks of treatment or after a dose increase.

What happens when you stop?

This is the question people don't ask until it's too late. In the trials, when people stopped semaglutide, most of them regained a large part of the weight within a year. Appetite comes back, and if eating habits haven't changed, the weight follows.

That doesn't mean you have to stay on it forever. It means the time on the medicine is the best time to build habits that last: regular meals, enough protein, portions you're comfortable with, and some daily movement. Those are what hold the result when the medicine stops.

Where a dietitian fits in

The medicine reduces your appetite. It doesn't teach you what to eat, protect your muscle, or plan for the day you stop. That's where I come in. Before you start, during the dose increases, and when you and your doctor decide to come off it.

If you're on one of these medicines, or thinking about it, bring your prescription and your latest blood tests to your appointment and we'll build the plan around them.