Weight loss & diet

Diet and weight loss pills, examined by scientists

Ever wonder what goes into weight loss pills, or whether they’re even safe? Here's what the science has to say.
Published 11 December, 2019

While every person’s weight loss journey is unique, there’s typically a common thread: the realisation that losing weight takes time and effort. There’s the food prep, the gym sessions, and the dedication to ditching unhealthy habits and behaviours.

If you're looking to drop pounds ASAP, weight loss pills may seem appealing. But could popping a pill really be the slim-down shortcut you’ve been looking for?

You’ve heard it before, but if something sounds too good to be true, it probably is, and diet pills are no exception. The pills (which include prescription medications, over the counter drugs, and dietary supplements) aren’t intended to be a fast, easy weight loss solution.

“They can be a helpful piece of the puzzle, but they’re not a quick fix,” says Kent Sasse, M.D., a bariatric medicine specialist in Reno, Nevada and author of The Type II Diabetes Cure. In some instances, these pills could even put your health at risk. 

How do weight loss pills work?

Weight loss pills work, or claim to work, in a number of ways depending on the product’s ingredients.

Some rev up metabolism to increase fat burn, while others curb your appetite or limit how much fat the body can absorb from foods, Dr. Sasse says.

Prescription vs. over the counter weight loss pills

Doctors sometimes recommend prescription weight loss pills, in combination with diet and exercise, to patients who have significant amounts of weight to lose, typically a body mass index (BMI) of 27 or higher. But you don’t need a prescription to stock up: many diet pills and supplements are sold over the counter.

Of course, that doesn’t necessarily mean they’re safe for everyone to take. In fact, some of these products can have scary health consequences, such as liver damage or heart trouble. You should always get the green light from your GP before trying a new medication or supplement, even if it’s one that you buy over the counter.

Are weight loss pills safe?

This depends. Approved drugs from registered sellers are likely to have gone through extensive clinical trials before being released to market. But as with all medications and supplements, diet pills can come with unpleasant or damaging side effects and risks, even if they’ve been tested and approved. In some cases, the long-term effects of taking these pills are unclear, while some are initially approved only to be withdrawn after a potential health risk comes to light. 

Buying weight loss pills online can also pose a health risk. One in 10 people in the UK have bought fake medical products online in the past year, according to the Medicines and Healthcare products Regulatory Agency (MHRA), which also found that 63% of people who had taken slimming pills they'd bought online experienced unpleasant side effects including diarrhoea, bleeding, blurred vision and heart problems.

To avoid unnecesary health risks (and potential credit card fraud) they recommend checking whether the seller is registered with the MHRA and authorised to sell medicines online.

Should you take weight loss pills?

Whether you should take prescribed medications is up to you and your GP. But when it comes to dietary supplements that are not overseen by the MHRA, or other over the counter diet pills, the side effects, financial cost, and unknown or potentially harmful impact on your long-term health is simply not worth the risk.

“The best case scenario from taking a diet pill for the purpose of weight loss - that is, losing a nominal amount of weight without developing any strategies to maintain the loss over time - is like asking a patient to put a plaster on a gaping wound,” says registered dietitian Jaclyn London, the Head of Nutrition at WW.

“The worst case scenario is side effects that make you feel physically sick, wasting money on a treatment that doesn’t work, and/or increasing your risk of potentially long-term health complications.”

What’s more, even an effective weight loss pill won’t address the underlying psychological factors that can contribute to a person’s weight. “Medication is a quick fix to a problem that requires a deep-dive into what contributed to weight-gain in the first place - environment, psychosocial factors, level of physical activity, history of disordered eating patterns, food and weight history, food security, exposure to nutrition education, genetic factors, and much, much more,” London says, adding that only certain instances warrant weight loss medications. “It’s worth an in-depth conversation with your GP.” 

That said, you and your GP should also consider the side effects and possible drug interactions before taking diet pills, and remember that there are certain people who should never take diet pills. If you’re pregnant or breastfeeding, have a history of disordered eating patterns, or have diabetes or are taking medication or insulin for the treatment of hyperglycemia, it’s best to steer clear.

As for the rest of us, the bottom line is: “There’s no such thing as a weight loss pill or supplement that can work in isolation of everything else you do all day,” London says. 

Not psyched about the prospect of potential health risks, stomach aches, nausea, and more? Dodge these reactions altogether by considering other weight loss methods, such as reducing calorie intake, engaging in physical activity, and following a healthy eating pattern. 

Reviewed by Jackie London, R.D., November 2019