"The worst kept secret in Hollywood!” shout the headlines. This particular badly-kept secret involves a pricey new weight-loss drug called Semaglutide. If you take the glossy celebrity magazines at face value, fans of these $1,200-a-month injections include Kim Kardashian and Elon Musk.


But in mid-February, the weight-loss treatment moved beyond the A-list when UK high-street chemists announced they would be selling Semaglutide injections from spring 2023. At the time of writing, the UK price had not been disclosed.

So what is Semaglutide? Is it safe? And could it be a game-changer for tackling the broader public health crisis of obesity?

What is Semaglutide?

Semaglutide is manufactured by the Danish pharmaceutical giant Novo Nordisk, and sold under the names Ozempic and Wegovy. Ozempic, in particular, made international headlines last year after going viral on TikTok, with the #MyOzempicJourney trend showcasing scarcely believable body transformations. Wegovy is the one going on sale in the UK.

Semaglutide is the latest in the line of analogues of GLP1, a gut hormone that signals to the pancreas to increase insulin secretion. Semaglutide and all its predecessors are, in effect, weaponised versions of GLP1, and were originally designed as treatments for type 2 diabetes.

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Their main superpower is that they survive for far longer in the blood than the GLP1 that occurs naturally in your body, which only has a half-life of two minutes. Earlier approved GLP1 analogues, including Exenatide from AstraZeneca and Liraglutide from Novo Nordisk, required daily injections. In contrast, someone with type 2 diabetes only needs to inject Semaglutide once a week, thus increasing insulin secretion and speeding the uptake of glucose from the blood into muscle and fat.

How does Semaglutide help you lose weight?

But wait a minute, what does any of this have to do with weight loss? Well, this is related to another function of GLP1 as a gut hormone.

Our brain needs to know two key pieces of information in order to control food intake. First, it needs to know how much fat we are carrying. Why? Because our fat is our long-term energy store, and is a marker for how long we would survive in the wild without any food.

The second piece of information our brain needs to know is how much and what we are currently eating, or have just eaten. These are short-term signals that come from our gut. Every time we take a mouthful of food, from the moment we begin chewing, until the moment it emerges from the other end, hormones are secreted. The vast majority of these gut hormones, including GLP1, make us feel full when they signal to the brain.

Therefore, a side effect of having a long-acting GLP1 analogue like Semaglutide hanging about, is that it signals to the brain and makes us feel full. What happens when we feel full? We eat less. What happens when we eat less? We lose weight. In fact, clinical trials with Semaglutide have shown that over two years of once-weekly injections, people lose, on average, 15 per cent of their body weight!

Is Semaglutide safe?

The results from the Semaglutide trials appear to indicate it is safe, certainly in the short- to medium-term. However, as with all drugs, there are side effects to consider. These have to do with yet another biological role of gut hormones, and that is to regulate the passage of food through our digestive system.

For example, when our body senses that it has ingested a toxin, gut hormones, including GLP1, are rapidly released. This sudden spike in gut hormones leads to the unpleasant and explosive ejection of the contents of our stomach, either upwards or downwards. Thus, side effects of Semaglutide can include nausea and diarrhoea. To be clear, most people do not get these side effects.

I believe that this drug could be a game-changer for the treatment of obesity. To lose 15 per cent of the body weight in two years is phenomenal.

A couple of things, though. First, should this drug be available, over the counter, for celebrities and others who can afford it? Given the effects on blood sugar levels, the issues with regards to dosing and side effects, and the limited data on long-term safety, Semaglutide and other similar compounds should only be available on prescription, at least for now.

Second, it is important to know that as with any other treatment, the moment you come off the drug, the weight will come back on. So for many people who medically qualify to receive Semaglutide, this is likely to be a treatment for life.

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Giles is a professor at the University of Cambridge, whose research focuses on food intake, genetics and obesity. He is a broadcaster and author, and his latest book is Why Calories Don’t Count (£14.99, Orion).