Wegovy, the weight-loss drug flying off the shelves

At his home in Denmark Casper Nielsen retrieves a package from the fridge and prepares to inject his next dose.

"So this is Wegovy, you take it four times a month," says the 45-year-old. "Before, I thought, 'maybe I'm not getting to be 60, maybe I'm not seeing my grandkids'.

"But now I'm looking at the future way brighter. [Two years ago] I started on 159kg [25 stone]... Right now, I'm weighing 93.5kg, so I'm in a really good place."

Fuelled by a social media buzz and celebrity users including Elon Musk, Wegovy is a weight-loss drug that has been flying off pharmacy shelves.

Such has been the rise in its global sales that its manufacturer, Danish drug-maker Novo Nordisk, last year became Europe's most valuable listed company.

"I think the only drug which it can be compared with is Viagra," says Kurt Jacobsen, a professor of business history at Copenhagen Business School, in reference to Wegovy's popularity.

Aimed at people who are severely overweight, Wegovy's active ingredient is a medicine called semaglutide, which helps control blood sugar, lowers appetite, and makes patients feel fuller. It is also the active ingredient in sister drug Ozempic, which is used to treat type 2 diabetes.

Research suggests that Wegovy patients can lose more than 10% of their body weight.

These issues have not slowed sales of Wegovy, which increased five-fold in 2023. It is currently available in eight countries - Denmark, Germany, Iceland, Norway, Switzerland, the UAE, the US and the UK - with Japan due to follow at the end of February.

In the UK it is now prescribed by some specialist NHS weight-loss management services, for patients who meet specific criteria. It is also available from some private clinics.

Meanwhile, Ozempic is now the world's biggest-selling diabetes drug.

The runaway sales of both drugs has led to surging earnings at Novo Nordisk. At the end of January it announced that its annual net profit had jumped by 51% to 83bn Danish kroner ($12bn; £9.6bn).

Speaking to the BBC, the firm's chief financial officer Karsten Munk Knudsen admits that Ozempic and Wegovy's huge popularity had initially caught the firm off guard.

"The demand in the market, both in diabetes and obesity, has just stepped up, much more than we ever forecasted. Much more than anyone forecasted," he says.

He expects those strong sales will continue in 2024, "we're guiding for 18 to 26% growth".

Whether Novo Nordisk can keep keep up with orders for Wegovy remains to be seen, says Emily Field, a pharmaceutical sector analyst at Barclays bank. "The underlying demand is so overwhelming, they can't make enough of it," she says.

Mr Knudsen acknowledges that the company won't be able to meet demand "any time soon", but adds that it is investing heavily to expand manufacturing capacity. "We're really building new facilities like never before."

For Denmark, a small country of less than six million people, Novo Nordisk is now so big that it's having an outsized impact on the Danish economy.

Denmark's economic growth was 1.1% over the first nine months of 2023. But strip away the pharmaceutical sector, dominated by Novo, and the economy shrank by 0.8%. The country is now publishing separate economic statistics, minus the drugs industry.

For almost a century, Novo Nordisk had focused on producing insulin. However the company has been transformed by its discovery of semaglutide in 2004. Several years later the medicine was developed as a treatment for diabetes, and the weight loss effect came as a surprise.

Ozempic was approved for sale in the US in 2017, and in 2018 in the EU. Wegovy followed in the US in 2021, and in the EU in 2022.

Dr Maria Kruger, a GP and spokesperson for the Danish Society for General Medicine, says that the number of patients now asking for Wegovy has "astonished" doctors, and she thinks that stronger guidance is needed for who should get it.

"Social media is really affecting people," she adds. "I think it's the idea we are having that the perfect body has to be slim and thin."

Conversely, she says that some people in Denmark who might benefit from taking Wegovy find it too expensive, as users in the country have to pay the full-market price for the drug.

"The patients who are really struggling with weight and maybe cannot work, and have physical disabilities, many of them cannot afford this drug," says Dr Kruger. "I think it's an inequality in health."

Meanwhile, some medical insurance providers in Denmark and the US are refusing to cover Wegovy due to concerns over its high price, together with rising patient numbers, and uncertainly over the length of treatment time.

Yet with worldwide obesity levels having almost tripled over the past 50 years, and tipped to hit one billion people by 2030, the success of Wegovy has set off a weight-loss drugs arms race.

Back in November, American pharmaceutical firm Eli Lilly was given clearance in the US to sell its rival Zepbound. Its sister drug aimed at treating diabetes, Mounjaro, was already on the market.

"Novo and Lilly have such a large head start," says Barclay's Ms Field. "Everyone's tripping hand over foot to catch up."

Novo Nordisk's Mr Knudsen shrugged off the increased competition: "The market potential is so big that there's more than enough space for two or even more competitors."

Back at Casper Nielsen's home in Zealand, he says that continuing to take Wegovy is keeping the weight off.

"Before I'd tried all the different kinds of diets a million times... and it was always the same, same story, I lost a lot of weight. And as soon as I let go of the diet just a little bit, I gained the weight in no time, and even a little bit more.

"But now I'm thinking, 'well, I'm gonna actually have my grandkids and I'm going to play with them'. I'm going to do all the things that a granddad should do."