The volume of people taking new and effective weight loss drugs has grown so big that it's shrinking food portions in the US

The impact of weight loss drugs around the world is so huge that big food companies are jumping in on the bonanza, targeting people on the medication with special food lines.

The self-injecting drugs like Ozempic, made famous by celebrities including Oprah Winfrey, are forecast to be worth $165 billion by the 2030s.

They're so popular the pharmaceutical giants can't keep up with the demand from millions of people around the world, which means New Zealand is missing out.

"New Zealand tends to be at the bottom of the list for pharmaceutical companies when it comes to supplying them," says Niki Bezzant, who writes about the boom in the Listener.

Even access to the Pharmac-funded drug Sexanda for people with type 2 diabetes is limited because of the squeeze on supply. And while drugs similar to Ozempic are available here they're not as effective in reducing weight and they cost $500 a month.

That's out of reach for most New Zealanders when they're expected to stay on them for the rest of their lives.

"If you start taking this for obesity then you're going to have to keep taking it to have the effect. You can't just go on it and then go off it," says Bezzant.

"It's the same as any other thing you might do for weight loss except for gastric surgery which is more permanent but even then can still fail."

The medical director of the New Zealand College of General Practitioners, Dr Luke Bradford, says more New Zealanders will be able to afford them as more versions of Ozempic and cheaper generics come on the market.

He says it is likely that within 10 to 20 years half of New Zealanders will be taking the drugs.

"We're going to see a real shift in their use and outcomes for patients over the next decade or so.

"I can see that down the line, and if we can improve the safety and the efficacy, that people will be on them if they need them and if their weight is high," Bradford tells The Detail. He notes however there is a significant proportion of people who can't take the meds because of side effects.

They include nausea, constipation, diarrhoea; gastroparesis and pancreatic cancer in rare cases, and possibly depression. But the drugs are also credited with preventing obesity-related cancers and heart disease.

Bezzant says the implications of the weight loss drugs boom go beyond the pharmaceutical industry. Already big food companies are responding as the appetites of millions of people shrink and US takeaway chains are also adjusting their offerings…

Go to this episode on rnz.co.nz for more details