The Truth About Diet Pills and Whether They Really Work

Diet pills are part of a multi-billion dollar weight-loss industry in Canada, but do they really work?

Diet Pills Really Work, woman holding diet pills and fruitphoto credit: shutterstock

The question we’ve all been dying to know – do diet pills really work?

They entice you with their labels – pictures of plump bellies shrunk to washboard abs – but do diet pills really work or are they just a bunch of hooey?

Diet Pills contain herbs and other natural ingredients and promise to “increase energy,” “burn fat,” “control appetite,” “flush fat” and more. Nobody keeps a tally of what portion these diet pills make up of the estimated 5 billion weight-loss industry in Canada. But there’s no doubt: Online and at drugstores, lots of us are buying hope in a bottle.

Like many women, though I exercise and eat a healthy diet, I’d love to lose that last stubborn five pounds with a pill. So I set out to find the truth about these concoctions.

What’s in diet pills?

Powerful laxatives

Take these – which carry claims that they “flush” or “melt” fat, and “cleanse” your body – and you’ll be spending a lot of time on the toilet. They tend to contain natural laxatives such as psyllium, rhubarb powder, cascara, fennel powder, senna, goldenseal and others, and natural diuretics such as ginger, fennel, vinegars and teas.

They come with warnings to drink lots of water and avoid taking other medication within two hours (because the desired effect of the other medicine may be reduced – something to consider if you’re taking anything from blood pressure meds to the pill).

That overuse can create a dependence on laxatives to move your bowels.


The labels claim they “burn calories,” “burn fat” and “increase metabolism.” They’ll likely make you feel jittery and on edge, and may cause your heart to race.

Common ingredients include caffeine, sometimes two to three cups of coffee worth in a single pill, and often green tea extract (listed as Camellia sinensis).

Appetite suppressants

These claim to kill hunger pangs and make you feel full. Peter Janiszewski, a Queen’s University PhD candidate and exercise physiologist, whose website Obesity Panacea debunks weight-loss products, observes: “High insoluble fibre tends to increase satiety, but it also creates gastrointestinal issues like gas, bloating and diarrhea.”

A common ingredient is hoodia, an African plant that some claim quells hunger (so far no research studies prove it’s safe and effective).

Green tea extract and psyllium are also commonly found in suppressants.

So, do diet pills really work?

Medical experts and pharmacists roundly say no. “If weight loss came in a bottle, the world would be slim,” says Dr. Yoni Freedhoff, a family doctor and the founder of Ottawa’s Bariatric Medical Institute, a leading centre for medically supervised obesity treatment.

When Freedhoff opened his clinic six years ago, he scoured the medical literature looking for a good herbal supplement to offer in addition to his program of medical assessment and counseling. “I’m still looking,” he says.

To date, he notes, no herbal preparations have been conclusively shown in well-designed, randomized, peer-reviewed trials to be both safe and effective for long-term weight loss. “Just because it’s natural doesn’t mean it’s safe,” says Freedhoff.

Dr. Arya Sharma, scientific director of the Canadian Obesity Network, agrees. “Laxatives and stimulants are not a healthy, safe approach to long-term weight management.”

Worse, they may be dangerous: In 2007, Health Canada issued at least 45 “risk communications” involving more than 170 weight-loss products, including the popular Hydroxycut in May 2009, which in the U.S. led to 23 cases of liver toxicity and one death.

The FDA told the company that since it was unknown what ingredient or combination of ingredients created the problem and who was at risk, any new formulation should get “a rigorous safety review” by the firm that markets it.

A reformulated product was back on shelves in months, and the company sent the FDA its new formulations and safety information. (The FDA won’t do a prior review of dietary supplements unless there’s an indication of a safety issue.)

Another Hydroxycut product, the Complete 7-Day Cleanse, was the subject of a Health Canada recall. The product contained a number of active ingredients with a combined effect that potentially posed serious health risks (e.g., dehydration and/or electrolyte imbalance).

Freedhoff and Sharma have called herbal weight-loss concoctions “snake oil” and have urged more stringent legislation preventing their sale until they’re proven safe and effective.

“Health Canada is failing Canadians,” says Freedhoff. “It’s an unregulated market.”

Health Canada’s response

Health Canada disagrees. Prior to 2004, it says, many health products made from herbs, spices and naturally occurring ingredients (known in Canada as “natural health products”) fell in a gap between pharmaceuticals and foods – they weren’t subjected to the same review standards.

In 2004, Health Canada’s Natural Products Directorate began assessment of some 45,000 vitamins, minerals and other supplements, including natural weight-loss aids.

Some 36,500 have so far been checked for safety, effectiveness and quality; of those, about 24,000 now have an eight-digit Natural Product Number or NPN (it appears on the label). Around 10,000 applications are still being assessed.

Many are assumed to be weight-loss formulations, but, says Health Canada, the number cannot be revealed for confidentiality reasons.

Products without an NPN can be sold until an assessment is done.

Their removal or investigation, says Christelle Legault, spokesperson for Health Canada, is triggered by formal consumer complaints, industry complaints, referrals from other provincial and federal regulatory agencies, international partners, observed contamination/adulteration, a suspected adverse reaction, or Health Canada’s compliance monitoring activities.

The National Association of Pharmacy Regulatory Authorities released a position statement that health products with no NPN should not be sold by pharmacists in the interest of public safety.

Adoption of this position is left to each province.

Are diet pills worth using after all?

I was curious to see how many of these products had an NPN, and what pharmacists thought. I asked three friends across Canada – in the West, Central and Atlantic Canada – to also go to drugstores and check it out.

None of the products we found – priced from $15.99 (on sale from $37) for a month’s supply, to $65 for a half-month’s supply – had an NPN, and every pharmacist in the dozen-plus stores we visited recommended we avoid them.

My friends took that advice; the products weren’t worth the risk or the cost.

I also took a pass, and that night, I bought green tea, went to yoga and made a Cobb salad for dinner. That felt like a much healthier approach.

Originally Published in Best Health Canada