Weight loss pills, also known as anti-obesity medications are pharmacological agents used to reduce or maintain weight by altering one or more fundamental metabolic body functions, most often appetite or absorption of calories.1 As such, they are significantly different from numerous weight loss supplements which can be used without prior consultations with a doctor, and which work through different modes, not having a direct impact on metabolic processes, but providing the body with different compounds such as proteins, vitamins, minerals or fatty acids which one might be lacking due to strict weight loss dietary regime.

What’s on this page?

Weight loss pills are usually prescribed by doctors to patients with body mass index indicative of obesity, that is, above 30, to prevent further health complications and conditions which might be caused by their condition. However, due to multiple known side effects of numerous diet pills, these medicaments are usually recommended only in those cases where the benefits outweigh the potential risks. It is also important to note than weight loss pills are always used in conjunction with other weight loss methods, the most important being diets and physical exercises.

What are weight loss pills?

While there are numerous brands of weight loss pills on the market, both prescription-only and over-the-counter, most of them are marked by the limited number of possible mechanisms of action. Because of this, we can classify most of the diet pills in four distinct groups, based on this criterion.

Norepinephrine–Dopamine releasing drugs

One of the earliest discovered groups of weight loss pills are norepinephrine–dopamine releasing agents which act by suppressing patient’s appetite thus diminishing the caloric intake and making the weight loss diets less unpleasant. This group includes amphetamine, phentermine, and related substituted amphetamines such as bupropion. However, it is important to note that NRDAs induce the release of norepinephrine, epinephrine and dopamine in the body and brain, which also makes them act as stimulants. Not only does this increases the chances for abuse, but also introduces potentially dangerous side effects.

Weight loss drugs that increase the body’s metabolism

This mechanism of action is rather straightforward – these compounds simply increase the number of calories you burn daily, so you just need to make sure that caloric deficit is successfully turned into visible weight loss. However, with relatively small benefits and even smaller number of clinical trials of these medicaments, results might either require dedicated dietary regime and exercise or be completely absent.

Weight loss drugs that inhibit fat absorption

Third and final big group of diet pills is based on an equally straightforward mechanism of action, but have proven to be successful in numerous clinical trials and scientific studies. These substances work by interfering with the body’s ability to absorb specific nutrients from food. The most widely used brand of weight loss pills of this type is Orlistat, which blocks fat breakdown in the digestive system by inhibiting pancreatic lipase, and by extension, blocking absorption of up to 30% of fat consumed through food. Other substances which can even be found in everyday groceries as food additives can have similar effect, like glucomannan used as thickener and guar gum, often used in baked goods and dairy products.

Experimental weight loss pills

Aside from these main types of diet pills, there are some which rely on unique mechanisms of action which are, either not thoroughly tested so far, or produce negligible results. For example, Rimonabant worked via specific blockade of the endocannabinoid system and this mechanism of action was inspired by the knowledge that cannabis consumers often experienced hunger as a side effect, so the developers of the medicine tried to somehow reverse the process. Although the initial results were promising, after clinical trials and numerous tests, the drug was withdrawn from the market due to significant safety concerns. Similarly to this, Sibutramine worked by acting on specific neurotransmitters in order to reduce the subjective sense of hunger. This approach proved to be successful at first but the project was later stopped when the trials highlighted significant adverse effects on cardiovascular system.

What are the best weight loss pills?

While it is relatively simple to classify diet pills into different groups, determining what is the best weight loss pill is a lot harder task and without a clear answer. This is mostly due to the fact that the choice of weight loss medication depends on numerous factors, including the nature of patient’s condition, the exact body mass index, previous or current medical conditions and complications, the amount of weight the patient wishes to lose, whether the weight loss should be short or long term, what is the nature of dietary regime and so on. So, the only way to find out what are the best weight pills for you is to consult with your doctor so he can make an informed decision and recommend the optimal choice.

Should I use weight loss pills?

Once again, the only way to get the right answer to this question is to consult with your doctor. However, there is a general agreement in the medical community that weight loss medications should be used only when benefits outweigh the risks. This means that in most cases, use of weight loss pills is not recommended, especially when you keep in mind that diet and exercise will, in any case, be a part of your treatment. Most of the time, weight loss pills are recommended to those with body mass index higher than 30, meaning they can be classified as obese, with their medical condition having an impact or a high probability of a future impact on health.

However, if you wish to shave off a couple of kilos before the summer vacation and you plan to get into exercising, while taking care of your diet, you can still choose some of the milder diet pills that are sold over the counter due to significantly lower likelihood of side effects, accompanied by less noticeable results. However, some of these diet pills, like Alli, can be rather helpful when combined with carefully developed exercise and diet plans, allowing you to get results quicker and get in shape before summer.

However, if you plan to use weight loss pills long term and reduce your weight by a significant amount, consultations with a doctor are highly recommended so you can get a weight loss plan customized specifically to you. In this way, you ensure both the optimal results and diminish the possibility of side effects.


  1. Obesity Prevention – NICE