All medicines have side effects, says Professor Rhiannon Braund, head of the University of Waikato’s school of pharmacy and biomedical sciences.
“When you’ve got a drug that acts in different parts of the body, it can have different reactions or different outcomes for people based on their physiology,” she says.
“That’s why dosing is really important because we’re all a little bit different. We’ve got different little quirks about all of us.”
All medicines have data sheets listing the known side effects ranging from common to rare, according to clinical trials. But those clinical trials are conducted on a narrow representation of the wider population.
“They don’t usually have trials with women. The risk of hurting or damaging an unborn child when these drugs are being tested is too high,” Braund explains.
“So they’re often on healthy males, and the side effects that are seen in the clinical trials [are in] that controlled environment. And so the side effects that we do see coming out afterwards are things that we couldn’t have predicted or we don’t know.”
Some of those effects are due to drug interactions, which can’t always be predicted in a clinical trial. It’s why Medsafe in New Zealand monitors medicines for side effects once they’re publicly available.
Prescribers are “hypervigilant” when it comes to the possible side effects of newly available medicines, Braund says.
“Nurses, doctors or pharmacists are always really mindful of talking to their patients about side effects when we don’t really know a lot about the medicines.”
What GLP-1s are available in New Zealand?
Semaglutide (Wegovy), dulaglutide (Trulicity) and liraglutide (Victoza, Saxenda) are available in New Zealand. Some are available on prescription for weight loss as well as for diabetes. Ozempic is another brand of semaglutide, which we don’t have here.
Pharmac has funded dulaglutide and liraglutide for type 2 diabetes, but not for weight loss – so those who are prescribed them for weight loss must pay for them.
The data sheets for the GLP-1s available in New Zealand list both their potential positive and negative side effects – here Braund explains why they occur, what you need to know and when to be concerned.
What are the positive side effects of these weight loss drugs?
GLP-1s offer some health benefits that come about as a result of weight loss, as well as other unexpected positives.
For many people, Braund notes, “it’s not just about physical weight – it’s about the consequences of carrying a little bit too much weight. It does have all of these other knock-on effects.
“Carrying a little bit more weight than we should does have problems for us around stroke and lots of other cardiovascular issues.”
Reduce risk of heart attack, stroke
Obesity increases the risk of a heart attack by straining the heart to pump harder, among other things. By triggering rapid weight loss, GLP-1s can lower that risk, as well as that of stroke.
Reduce risk of fatty liver disease
They can also reduce your risk of fatty liver disease, which is caused by fat build up in your liver, and of lipid disorders – an unhealthy balance of the fats in your blood.
Lower blood pressure
GLP-1s can help lower blood pressure through weight loss as excess body fat makes the heart work harder. The drugs also help your kidneys get rid of more salt and improve blood vessel function.
Reduce risk of kidney disease, diabetes-related nephropathy or kidney damage
GLP-1s can slow the progress of kidney disease and lower risk of kidney failure, though experts say nutritional support is essential with this.
Reduce risk of seizures
Studies have suggested that GLP-1s can reduce the risk of seizures, though more research is needed.
Help with addiction
GLP-1s suppress the hunger hormone, so can help with food addiction. Following that logic, some researchers have suggested they could be used to curb other addictions, such as to alcohol or opioids.
Help with obstructive sleep apnoea
Even minor weight loss can make a difference to those with sleep apnoea, Braund says.
“When you’ve got sleep apnoea, you wake up more tired than when you went to bed.”
Benefits for PCOS
GLP-1s may have benefits for people with PCOS (polycystic ovarian syndrome) by lowering insulin resistance and regulating hormones and ovulation.
Weight loss as a result of using GLP-1s could help “the body regulate all of those things a little bit better,” Braund says.
For the same reason, they may improve fertility. That’s partly because obesity can impact fertility in both men and women, so rapid weight loss can boost it. If you’re on the contraceptive pill, GLP-1s can affect how well it works as it slows the absorption into your body.
It’s unknown whether GLP-1s are safe to use in pregnancy.
What are the negative side effects?
Nausea, vomiting, diarrhoea, indigestion, constipation
GLP-1s commonly cause gastrointestinal symptoms, because they slow down the emptying of your stomach and affect the part of the brain that triggers vomiting.
“Most of [those] are quite mild and they resolve quite quickly,” Braund says.
“You can modify that by what we call dose titration, so lower dose, and then people get more used to it.”
Bone fractures and muscle loss
Some research has suggested GLP-1s increase the risk of bone fractures due to a reduction in bone mineral density due to weight loss, while other studies have found no risk.
And according to research from Mass General Brigham (based at Massachusetts General Hospital) any form of weight loss can see people experience muscle loss – not just during the use of GLP-1 medication.
“In simple terms, when you lose weight, you are decreasing caloric intake in terms of proteins, carbohydrates, and fats,” says Dr Caroline Apovian, one of the researchers. “The brain needs glucose. Fat by itself cannot be turned into glucose, and that is the major reason why muscle loss is inevitable when you decrease caloric intake.”
Their research found combining a high protein diet with consistent exercise while on GLP-1s, has the greatest benefit in preserving bone and muscle mass, compared to either technique being used alone.
You need 0.8g-2.2g per kg of your body weight in protein each day – find out more about how to get it here.
Headaches and dizziness
These commonly occur when starting GLP-1s as the body adjusts to the drug and usually ease with time.
Mild tachycardia (increased heart rate)
Another common side effect that is usually harmless. Staying active and limiting alcohol and caffeine can help. Monitor if you have an existing heart condition and if you experience palpitations or chest pain, tell your doctor.
Upper respiratory tract infection
This is listed as a common side effect of some GLP-1s available in New Zealand. It hasn’t been proven that GLP-1s cause these infections, but they can be associated with the symptoms.
GLP-1s can cause acid reflux, which can irritate your throat. They also stimulate your vagus nerve, which helps control your immune system as well as your digestion and heart rate.
This side effect also usually subsides over time.
Hair loss
Hair loss is listed among the common side effects of Wegovy. But as Braund notes, “It’s hard to know [if this] is actually from the drug [or if this] just happens at the same time.”
That’s why when medical assessors look at reported side effects, they consider the “temporal relationship” – when the effect occurred in relation to when the drug was taken.
“Did that happen in a logical time-wise fashion?”
Injection site reactions
Some people may find their skin reacts at the site where they’re injecting themselves, whether they’re on a daily or weekly dose.
“They’re not painful injections, but we would encourage people to rotate where they do them,” Braund says.
In the future, an oral version may be available in New Zealand, which would remove this risk.
Hypoglycaemia
Low blood sugar is a common side effect in people on GLP-1s who also have type 2 diabetes.
Gastroparesis/stomach paralysis or delayed gastric emptying
GLP-1s slow down your digestion, which in some people can become excessive and leave the stomach muscles unable to work properly – though this is rare, according to the drugs’ data sheets.
Gallstones or gall bladder inflammation
GLP-1s also slow down the gall bladder’s emptying of bile, and may be associated with an increased risk of gallstones, another rare side effect.
Pancreatitis
A rare side effect of GLP-1s is pancreatitis, which is inflammation of the pancreas causing severe pain in the upper abdomen, nausea and vomiting.
Recent studies show the risk is minimal, though it’s important to monitor the above symptoms and see your GP if you have concerns.
Potential increased risk of diabetic retinopathy, NAION
According to the American Academy of Opthalmology, vision loss is a rare potential side effect of GLP-1s, though more research needs to be done.
Recent studies suggest GLP-1s can potentially increase the risk of two types of vision loss: diabetic retinopathy and non-arteritic anterior ischemic optic neuropathy (NAION). Diabetic retinopathy is listed as a possible side effect on the data sheets for the GLP-1s available in New Zealand.
“It’s still an evolving space, and the information we think we’ve got now isn’t the information we’ll have three months from now,” Braund says.
What to do if you experience negative side effects
If you find yourself experiencing unwanted side effects on GLP-1s, you can go back to your prescriber for help in managing them, or report them to Medsafe directly.
“Medical assessors will go through them and find out if there’s something that we need to be more concerned about,” Braund says.
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”.
Speaking to the Herald earlier this year, Dietitians New Zealand spokesperson and registered dietitian Lily Henderson said wraparound support is needed for those on GLP-1s to ensure they’re not missing out on key nutrients.
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.
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