How do GLP-1s work and what are the common side effects?
GLP-1 drugs work by imitating the gut hormone glucagon-like peptide 1, which suppresses the appetite, slows down digestion, and helps release insulin.
The known side effects are largely gut-related – constipation, diarrhoea, reflux – and usually ease with time, depending on the dose.
Professor Rhiannon Braund, head of the University of Waikato’s school of pharmacy and biomedical sciences and a practising pharmacist of 25 years, says all medicines have side effects – most of them minor.
“But there are often a small number of side effects that are more severe, and only occur in a small number of people,” she says.
“When a medicine with a small, significant side effect is taken by a lot of people, they appear to be more common. So, rare side effects when taken by large numbers of people are more noticeable.”
Singer Robbie Williams says taking weight loss medication made his vision worse. Photo / Getty Images
With GLP-1s, there has been a noticeable shift in the past few years, she says.
“Everyone knows about [GLP-1s’] use for diabetes, and then they have this bonus effect of helping with weight loss – which is why a lot of them are being used off-label, or in a particular way,” she says.
“That’s really been the big drive for its use internationally. We’re starting to see it here.”
Is vision loss a side effect we should be worried about?
“The American Academy of Ophthalmology lists vision loss as a rare potential side effect of this class of medications,” Braund says.
Two new studies on this topic, presented at the annual meeting of the American Academy of Ophthalmology last month, showed mixed results.
One found that GLP-1s can increase the risk of two types of vision loss: diabetic retinopathy and non-arteritic anterior ischemic optic neuropathy (NAION). The other showed they might actually help prevent dry age-related macular degeneration (AMD).
Both studies concluded that more research is needed on GLP-1s and how they affect eye health.
Professor Rhiannon Braund is the head of the University of Waikato’s school of pharmacy and biomedical sciences.
What else should we know about weight loss drugs?
In New Zealand, weight loss drugs can be prescribed by your GP if you meet certain criteria, with BMI, age, and health issues such as diabetes or high blood pressure taken into account, and haven’t seen weight loss as a result of lifestyle changes. They are unfunded and can cost up to $600 a month.
For people who do qualify, these drugs can be “really effective”, Braund says.
“They are at risk of the same side effects as everyone else, but when you’re under medical care, it’s quite a different proposition. So if you do start to have these side effects early, you can modify the dose, or there are other things that can be done.”
That’s why it’s important to use them with clinical oversight, so that if you are worried about any side effects, you can speak to your prescriber.
“If you notice these side effects, the best thing if it’s severe is to stop the treatment and then go back for another evaluation.”
Most side effects are mild and transient – meaning they aren’t serious and will go away.
“[With] those rare side effects, they are rare, but they are real. Most people can expect to have very limited problems with this medicine, but it’s always about being vigilant,” Braund says.
“Sometimes it’s really hard to predict who’s going to get one of the more random side effects. People shouldn’t be scared of taking these kinds of medicines, but with any medicines, it is worthwhile making sure you know what the risks are.”
According to Ministry of Health clinical guidelines for health practitioners around weight loss management, “people should always use weight-loss drugs in conjunction with lifestyle changes”.
“Clinical trials are showing the best results happen when you are a little bit more active, and a little bit better with your diet,” Braund adds.
“You don’t have to change everything and become a fitness fanatic, but those small changes alongside medicines like this can make a really big difference.
“When you stop [taking them], there can be a little bit of rebound weight gain – so if you are doing this alongside making some better lifestyle and health choices, then that won’t be such a problem for you.”
Bethany Reitsma is a lifestyle writer who has been with the NZ Herald since 2019. She specialises in all things health and wellbeing and is passionate about telling Kiwis’ real-life stories.