LONDON - The World Obesity Federation has warned that more than half the world’s population will be classed as obese or overweight by 2035 if authorities do not act now. The report says that more than four billion people will be affected, with rates rising fastest among children, and in low or middle-income countries in Africa and Asia. The organisation forecasts that the cost of obesity will rise to more than $4 trillion (£3.3 trillion) annually by 2035. It comes as the demand for obesity drugs continues to skyrocket in the Western world.

Tirzepatide and the other ‘breakthrough’ obesity drugs

A new weight-loss medication “could become the best-selling drug of all time” with annual sales forecast to hit $48 billion, according to reports.

Tirzepatide will be granted approval by the US Food and Drug Administration (FDA) within months, reported NBC News. It is the latest in a string of obesity drugs that are being hailed as breakthroughs – but how safe and affordable are they?

How does the drug work?

The drug, sold as brand name Mounjaro and already approved to treat diabetes, is classified as a GLP-1 agonist, as are two other recently approved weight-loss drugs on the market, Wegovy and Saxenda, both of which are from the Danish drugmaker Novo Nordisk.

Given as an injection, all three mimic a hormone that helps reduce food intake and appetite. However, tirzepatide also imitates a second hormone, which may also improve how the body breaks down sugar and fat.

The results are eye-catching: in a phase 3 clinical trial, a high dose of tirzepatide helped patients lose 22.5% of their body weight on average, or about 52lb. This is “better than any medication currently on the market”, said NBC.

The drugs work by stimulating the release of insulin, which helps lower blood sugar, said CNN, and also slow the passage of food through the gut. “It leaves you feeling full pretty much all of the time,” a user of a GLP-1 agonist told the broadcaster. “You don’t want to eat.”

An expert described the emergence of the drug as “remarkable” and “revolutionary”. In a blogpost Eric Topol, executive vice-president of Scripps Research, wrote that “we now have a breakthrough class of drugs that can achieve profound weight loss equivalent to bariatric surgery”.

But is it safe?

Opinion is divided on the safety of the drugs. Gizmodo said that “many, but not necessarily all”, experts agree that semaglutide, the active ingredient in Wegovy, can “lead to sustained and safe weight loss, along with many other possible health benefits”.

The drugs are gaining approval from the authorities. Analysts are confident that tirzepatide will be granted approval by the FDA this year, said NBC. Meanwhile, noted Gizmodo, the FDA has expanded the use of Wegovy to children as young as 12, in “the latest success for this new generation of obesity treatments”.

However, they carry gastrointestinal side effects, “can cause low blood sugar and have a possible association with an increased risk of pancreatitis and some cancers”, according to the Mayo Clinic, reported Axios.

There is also concern that the popularity of the medicine could have a knock-on effect on those with diabetes, noted CNN. Since the diabetes drug became a “hot new weight loss fad”, diabetics are “having trouble finding it”, said the broadcaster.

How much does it cost?

The drugs can cost up to $1,500 a month and many users will need to keep taking it to maintain their new lighter weight.

The main problem is that demand is exceeding supply. With at least one in three American adults meeting the definition of obese, there is intense interest in the medication, which has spiked prices.

“The demand exceeded the expectations any of these drug manufacturers could’ve imagined,” Amanda Velazquez, from the Cedars-Sinai Center for Weight Management and Metabolic Health in Los Angeles, told CBS News.

Wegovy has been in “short supply since its debut”, said Gizmodo, due to unexpected demand and production issues that caused the temporary shutdown of a key manufacturing facility.

The new raft of anti-obesity drugs “will remain out of reach for many people, due to their hefty price tag”, it added, as insurers in the US are reluctant to cover the cost of the drug.

Meanwhile, Khloe Kardashian has denied using the diabetes medication Ozempic, which contains semaglutide, to reduce her weight, said

Under an Instagram post from the celebrity, a follower commented: “The fact that she uses diabetic medicine to get this skinny is disturbing.” Kardashian quickly replied: “Let’s not discredit my years of working out. I get up 5 days a week at 6am to train. Please stop with your assumptions. I guess new year still means mean people.”