Orlistat, both in its prescription and non-prescription form, is used in conjunction with individualized diet and exercise programs in order to aid individuals in losing weight in a safe and reliable manner. Thoroughly tested and studied, Orlistat is the only weight loss drug approved by European Medicines Agency and is used worldwide under several brand names. With fast and noticeable, albeit modest, results, the prescription form of Orlistat is usually recommended to patients with body mass index in the obese range, that is higher than 30. Exceptions can be made when patients aren’t clinically classified as obese, but have medical conditions which are known to be caused, worsened or associated with obesity in some other way, such as high blood pressure, diabetes or high cholesterol. However, in overweight yet otherwise healthy individuals, the non-prescription and less concentrated form of Olistrat is usually recommended.

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What is Orlistat?

Orlistat is a weight loss drug classified as reversible gastrointestinal lipase inhibitor which produces slimming effects by reducing the caloric intake, or more specifically, by inhibiting the absorption of up to 30% of fats from every meal in its 120mg prescription form, and up to 25% of fats in non-prescription 60mg form.1

Official chemical nomenclature for Orlistat is (S)-2-formylamino-4-methyl-pentanoic acid (S)-1-[[(2S, 3S)-3-hexyl-4-oxo-2-oxetanyl] methyl]-dodecyl ester, making it a single diastereomeric molecule that contains four chiral centers, with a negative optical rotation in ethanol and an empirical formula of C29H53NO5.

A saturated derivative of lipstatin, a potent natural inhibitor of pancreatic lipases isolated from the bacterium Streptomyces Toxytricini, Orlistat has the same therapeutic, weight loss properties as its parent compound, but is at the same time much more stable and easily reproduced2 , making it a perfect choice for an active ingredient of new generation of weight loss drugs.

How does it work?

With minimal systemic exposure, the absence of absorption or accumulation in the organism and almost non-detectable traces present in the blood, Orlistat stands out from the competition by acting exclusively locally, in the lumen of the stomach and small intestine. Its mechanism of action includes forming a covalent bond with the active serine residue site of gastric and pancreatic lipases, thus inhibiting these enzymes from hydrolysing dietary fat in the form of triglycerides into absorbable free fatty acids and monoglycerides, thus producing a caloric deficit.

Human organism cannot directly absorb triglycerides. Instead, it relies on pancreatic and gastric lipases to break them down into compounds it can absorb. But, with the presence of Orlistat, these enzymes remain inactive, and unabsorbed triglycerides are excreted unchanged. In this way, Orlistat blocks up to a third of fat contained in every meal.

How is Orlistat used?

Both in their prescription and non-prescription form, Orlistat weight loss medicines are used orally, in form of pills three times a day before each meal with or without water. If you missed a dose, you can still take it if less than an hour has passed since the last meal. If that is the case, you’ll still get the desired, although somewhat diminished effect. However, if more than an hour has passed, skip that dose and continue with the regular treatment routine.

This routine can be somewhat changed in rare occasions and if that is the case, be sure to consult your doctor about the individualized treatment routine. However, for most, three pills a day will be recommended. It is worth noting that increased dosage does not produce increased weight loss effects, but can lead to more pronounced side effects which is why both the medical community and the manufacturers strongly advise against this practice.

It is also very important to note that despite the fact that Orlistat is known for being effective and reliable, it cannot produce visible results in itself. In both prescription and non-prescription form, Orlistat must be used in conjunction with other weight loss efforts, most importantly physical activity and dietary regime. For branded Xenical, your doctor will usually recommend you the individualized weight loss routine which should help maximize the effects of the drug, while minimizing the adverse effects and keeping you healthy and in shape. And if you’re using the non-prescription form, Alli pills, it is still highly advisable to consult with your doctor, nutritionist or personal trainer in order to ensure visible and long-term weight loss effects.

Orlistat contraindications and side effects

There are some cases in which Orlistat treatment should be avoided, like during pregnancy or in patients with chronic malabsorption syndrome, cholestasis or known hypersensitivity to Orlistat. It is also worth mentioning that during Orlistat treatment, the absorption of other fat-soluble nutrients is also inhibited, so it is advisable that the patients take a multivitamin tablet containing vitamins A, D, E, K and beta-carotene once a day, before bed, to make up for the deficit in these nutrients.

Side effects of Orlistat are well known and documented thanks to numerous studies and clinical trials aimed at identifying them. While they can be rather unpleasant and can lead to the termination of treatment in up to 8.8% of patients in the trials, they are strictly localized to gastrointestinal adverse effect and usually last between one and four weeks since the beginning of treatment. Olistrat side effects manifest in up to 50% of patients in clinical trials and most commonly include oily stool, flatulence, fecal incontinence, and frequent or urgent bowel movements.

Is it the right option for me?

Orlistat, in itself, is an active ingredient found in different medications, most notably prescription-only 120mg Xenical and over-the-counter 60mg Alli. The prescription form of Orlistat can be suggested only by your doctor and this recommendation is usually issued only in certain circumstances – when body mass index exceeds obesity limit or when there are other obesity-linked conditions present in an overweight patient. With doctor’s prescription, the patient will usually get a detailed and individualized weight loss plan that includes exercise and diet plan that will help maximize the results of the treatments while diminishing adverse effects.

However, if your body mass index isn’t in the obese range, but you’re still looking for some medication that will help you shave off those extra few kilos before you hit the beach, Alli pills might be the better choice for you. However, it is worth noting that despite the fact that Alli is sold over-the-counter worldwide, it is still beneficial to consult with your doctor before starting the treatment.


  1. Evaluation of Efficacy and Safety of Orlistat in Obese Patients – NCBI
  2. Syntheses of Tetrahydrolipstatin & Configuration of Tetrahydrolipstatin & Lipstatin – Wiley