Weight loss pills: how do they work and how effective are they at losing weight?

At the counters of the pharmacy, we can find a multitude of over-the-counter weight loss pills: fat burners, fat caps, orlistat, etc. But do they really work? What do you have to do to get the desired results? We’ll explain it to you.

According to the “European Regional Obesity Report 2022,” published by the Office of the World Health Organization (WHO), 59% of European adults are overweight or obese, and almost all countries exceed rates by 50%.

Spain ranks 9th out of 53 countries with a 60% obesity rate.

These figures give us an idea of the epidemic proportions that obesity has reached and also explain why pills that promise to help you lose weight quickly are so in demand.

Are weight-loss pills effective?

The sale of weight-loss products is the most popular in pharmacies. According to Dr. Diego Bellido, a doctor specializing in endocrinology and nutrition and former vice president of the Spanish Society for the Study of Obesity (SEEDO), spending on treatments for obesity amounts to almost 20% of global pharmaceutical expenditure.

But what do experts think about weight-loss pills that are sold without a prescription? For Bellido, there are no serious clinical trials that demonstrate its effectiveness.

That, he says, does not imply that at a specific level, Weight loss pills: how do they work and how effective are they at losing weight? there are people who believe their use is going well, but “they are subjective situations, which do not have any statistically significant impact at the population level,” the endocrinologist clarifies.

Rosa Arnau, president of the Official College of Pharmacists of Castellón, says, “Almost always, in addition to the pill, a change in lifestyle is needed to get the results you want.”

“Diet with a change of habits and regular exercise are the foundation of the treatment,” says Dr. Bellido.


The claim of certain pills and supplements for weight loss is that, thanks to them, metabolic expenditure increases.

  • If we take a look at its ingredients, we see that they usually carry natural substances that are considered thermogenic, such as green or red tea, green coffee, guarana, or caffeine.
  • Again, eating right and exercising will boost your metabolism.

Since they are stimulant substances, you should not take them if you have a hard time sleeping.

  • For Bellidono, there is no drug that has this thermogenic effect because it would make the heart beat very fast.

Despite this, “it is a very interesting line of research for the future,” says the expert.

How do the capital pills work?

Weight-loss pills that promise to block and capture fat are another of the most popular options. The three most common active ingredients in this type of pill are:


L-carnitine allows fats to reach mitochondria, which use them for energy, according to Rosa Arnau (that is, burning them).

This substance works as a fat burner, but only in amounts of about 4 grams per day (which are considered very high) and after a sustained intake of more than six months.” “From then on, its effects begin to be noticed, but only when you exercise intensively,” says the pharmacist.

Weight loss pills with Chitosan

This part comes from the shells of crustaceans and can soak up fats “like a sponge,” says Arnau.

After that, the intestinal flora consumes them in the large intestine, releasing gases

What is Orlistat?

It is the active ingredient of an obesity drug that has two versions: a more powerful one, which is sold over the counter, and a softer one, which can be bought without a prescription.

It is a derivative of lipostatine, a substance that inhibits the enzyme that cuts fat (lipase) in the intestine.” “Since they are not cut, they cannot be absorbed and are eliminated by the stool,” explains Rosa Arnau.

The expert also tells us that it can cause side effects such as fatty diarrhea, an urgent need to go to the bathroom, nausea, vomiting, headaches, or even depressive problems.

How long can you take the pills to lose weight?

It depends, above all, on the composition. Although, as the pharmaceutical company emphasizes, “they are certainly not intended to be consumed chronically.” “It is best to follow the manufacturer’s instructions and the advice of our doctor or pharmacist.”

Keep in mind that, although they are sold without a prescription,…

  • If you’re pregnant, breastfeeding, have diabetes, high blood pressure, heart disease, or a thyroid issue, don’t use it.

    If you have intestinal inflammation or constipation, don’t take these.

People with hypertension or thyroid disorders should not take them.

  • Grasply pills can interact with other drugs and reduce the efficacy, for example, of birth control pills and preparations used in the treatment of menopause. “To avoid this, you have to allow at least four hours between the consumption of both,” warns Rosa Arnau.

“They can aid in long-term therapies, but keep in mind that they are a supplement and not the major mechanism for losing weight,” the pharmacist says.

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