What is Orlistat?

Orlistat is a prescription weight-loss medicine for adults aged 18 or over who are clinically overweight or obese. It belongs to a group of medicines called lipase inhibitors and works in the digestive tract to block the enzymes that break down fat. By preventing the absorption of up to 30 % of dietary fat, those calories pass through the gut and are excreted naturally.

In the UK, Orlistat is available as 120 mg capsules on prescription (brand name Xenical or generics) and as a 60 mg over-the-counter product (Alli). At 123Meds we supply Orlistat 120 mg capsules on prescription only.

What is Orlistat Used For?

Weight loss and maintenance – for adults with a BMI of ≥ 30 kg/m², or ≥ 28 kg/m² if you have weight-related conditions such as type 2 diabetes, high blood pressure or raised cholesterol.

Improving weight-related health risks – by lowering calorie intake, Orlistat can help improve blood sugar control, blood pressure and cholesterol when combined with a reduced-calorie, lower-fat diet and regular physical activity.

Note: Orlistat is not a “quick fix.” It is most effective as part of a comprehensive weight-management plan that includes a balanced, lower-fat, calorie-controlled diet and regular exercise.

How Orlistat Works?

Orlistat acts locally in the gut with minimal absorption into the bloodstream.

Blocks fat absorption: inhibits gastrointestinal lipases so around 30 % of fat passes through undigested.
Fat excretion: unabsorbed fat leaves the body in the stool, reducing overall calorie intake.

This targeted action supports gradual, sustainable weight loss.

When is Weight-Loss Medication Like Orlistat Needed?

Your prescriber may recommend Orlistat if you:

Have a BMI ≥ 30 kg/m², or ≥ 28 kg/m² with weight-related conditions such as type 2 diabetes or hypertension.
Have tried diet and exercise for at least three months without sufficient weight loss.
It is prescribed when lifestyle changes alone have not achieved adequate results and excess weight poses significant health risks.

Can Orlistat Be Purchased Over the Counter?

In the UK only the 60 mg dose (Alli) is available without a prescription and for adults with a BMI ≥ 28 kg/m².

The 120 mg strength (Xenical or generic) is prescription-only.

At 123Meds a prescriber will review your health, BMI and medical history to confirm whether 120 mg Orlistat is suitable.

Alternative Weight-Loss Medications

If Orlistat is not right for you, other options may be considered:

Wegovy (semaglutide): a once-weekly injection that reduces appetite and supports blood-sugar control.
Mounjaro (tirzepatide):a once-weekly injection that reduces appetite and supports blood-sugar control.

Your prescriber will help decide which treatment best suits your needs.

How to Take Orlistat 120 mg

Dosage: One 120 mg capsule three times daily with each main meal that contains fat.

Timing: Take during the meal or within one hour after eating so the medicine is present while fat is being digested.

Meal composition: Aim for meals with about 15–19 g of fat and distribute fat intake evenly across the day.

Skip if no fat: If you miss a meal or eat a fat-free meal, skip that dose—never double up.

Vitamin supplements: Because Orlistat can reduce absorption of vitamins A, D, E and K, take a multivitamin at bedtime or at least 2 hours after an Orlistat dose.

Review: If you have not lost at least 5 % of your body weight after 12 weeks, your prescriber will reassess treatment.

Diet & hydration: Maintain a reduced-calorie, lower-fat diet and stay well hydrated.

Active ingredient: Orlistat 120 mg.

Inactive ingredients (may vary by manufacturer): sodium starch glycolate, microcrystalline cellulose, povidone, talc; the capsule shell may contain gelatin and colouring agents.

Always read the patient information leaflet (PIL) in your pack for the complete list of ingredients, and to check for any you might be allergic to.

Orlistat is generally well tolerated but can cause side effects, mostly related to the digestive system and more common with high-fat meals.

Common effects:

Oily or fatty stools
Urgent or increased bowel movements
Flatulence with discharge
Abdominal cramps or discomfort
Soft stools or rectal irritation
Occasional headache
These usually lessen with a lower-fat diet.

Serious (seek urgent medical help):

Severe abdominal pain (possible gallbladder or pancreatitis)
Signs of liver problems: yellowing skin/eyes, dark urine, persistent fatigue
Severe skin reactions (blistering, peeling)
Severe allergic reactions (swelling of face/lips/throat, breathing difficulty)
Rarely, Orlistat may increase the risk of kidney stones or oxalate nephropathy—tell your prescriber if you have kidney disease.

If you experience any serious or persistent side effects, please seek urgent medical evaluation from your GP, NHS111 or by calling 999.