What to know first taking Weight-loss drugs 

Millions of people like are now accessing medications like semaglutide and tirzepatide, better known by their popular brand names Ozempic and Mounjaro. The numbers of people on weight-loss medication is only likely to increase as new drugs appear on the market too, including pills rather than the current jabs.

Weight-loss drugs are not the quick fix solution that many people believe, especially if you hope to keep the pounds off in the long-term.

It's clear that these drugs are opening up a new era in the treatment of obesity. The condition, is now a "mitigatable" issue, David Cummings, professor of medicine at the University of Washington tells me. "They are the closest thing I've seen to miracle drugs".

Other academics, however, warn that we risk losing sight of the need for behavioural change, especially as weight tends to be regained quickly when people stop taking the drugs.

So what should anyone planning to use weight-loss medication consider before they start?

How they work

Weight-loss drugs work by suppressing an individual's appetite by mimicking hormones that tell our body when it is full. The most common are known as glucagon-like peptide 1, or GLP-1, and glucose-dependent insulinotropic polypeptide, or GIP.

The drugs bind to specialised molecules on the surface of our cells known as GLP-1 and GIP receptors, which play a key role in telling our body when it has had enough food.

Typically someone taking these drugs will begin to lose weight within the first few weeks. Although the drugs are only approved for weight loss in people with obesity, there is a rapidly growing private market for those not considered clinically obese.

Their popularity has been rising because they are extremely effective, with weight loss of between 14-20% in 72 weeks. But about 10-15% of people lose very little weight, so called "non-responders".

GLP-1s are like "a chemical shield" that protects individuals against our "modern obesogenic environment, filled with cheap, calorie-dense foods", says Naveed Sattar, a professor of cardiometabolic medicine at the University of Glasgow and leads the UK Government's Obesity Healthcare Goals programme. He has also consulted on medical trials with several companies who produce weight-loss drugs but does not own any shares.

"There's food everywhere," he says – and within half an hour anyone "can pick up the phone and order 10,000 calories of food".

If you stop, you'll gain weight

If someone living with obesity starts to take weight-loss drugs, they need to consider that they may be on the drug long-term, says Cummings, who runs a weight management programme for individuals with obesity who have BMIs of 50 and above.

A common question he is asked by his patients before they start taking a weight-loss drug is how long they will be on it. Typically, they stop taking the drugs after about a year, he says. One analysis of scientific studies involving more than 9,000 patients indicated the average treatment duration was 39 weeks. People believe they can continue to lose weight using their willpower, he says, but the evidence suggests that is not the case.

People stop for various reasons, either due to the expense of treatment, their insurers stopping coverage or individuals not wishing to be on drugs for a prolonged period of time, Cummings has found.

And when people do stop the drugs, their weight tends to rebound. A recent study found that weight regain happens up to four times more quickly after stopping weight-loss drugs compared to someone ending a weight-loss programme that focuses on changing their behaviour.

Another study found that those on weight-loss drugs gained 1.5kg (3.3lbs) eight weeks after they stopped the medication, with their weight continuing to climb with the more time that passed. The same study also found that other health concerns, such as high blood pressure, also returns. New research has also found that people who stop taking weight-loss drugs gain back around 60% of the weight they lost a year later.

It returns quickly because of something researchers call "food noise", which consists of persistent and intrusive thought around food, says Sattar.

Hormones play a role too. When an individual tries to lose weight, it triggers a powerful hormonal response that tells your body to regain the weight you lost. Cummings explains that because of this, the brain interprets a calorie drop as an energy deficiency, so after stopping weight-loss drugs, hormones that stimulate appetite increase while the rate at which you burn energy – the metabolic rate – decreases. "If these biological defences are strong enough, they can blunt the drug's effectiveness," he says.