Orlistat

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Orlistat on Prescriptsy

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Orlistat 120 mg is a lipase inhibitor used as an adjunct to a reduced-calorie diet and exercise for the management of obesity.

It works by blocking the action of lipase enzymes in the gut, preventing approximately one third of dietary fat from being absorbed.

The undigested fat passes through the bowel and is excreted.

Orlistat 120 mg is a prescription-only medicine (POM) in the United Kingdom, while a lower-strength 60 mg formulation (Alli) is available as a pharmacy (P) medicine without prescription.

Orlistat was originally developed by Roche and is now available as a generic medicine from multiple manufacturers.

Obesity is one of the most significant public health challenges in the United Kingdom.

According to the Health Survey for England, approximately 26 percent of adults are obese (BMI 30 or above) and a further 38 percent are overweight (BMI 25 to 29.9).

Obesity significantly increases the risk of type 2 diabetes, cardiovascular disease, hypertension, dyslipidaemia, non-alcoholic fatty liver disease, obstructive sleep apnoea, osteoarthritis, and several cancers.

The economic burden on the NHS is substantial, with obesity-related conditions costing an estimated 6.5 billion pounds annually.

This page provides a comprehensive clinical guide to orlistat 120 mg, including how it works, dosage instructions, side effects, safety warnings, and how to obtain it in the United Kingdom.

Important safety information about orlistat

Before reading further, please note these essential safety points.

• Orlistat works only when taken with meals containing fat. It is not effective if taken on its own.
• Keep dietary fat below 30 percent of total calories to minimise gastrointestinal side effects.
• Take a daily multivitamin (containing vitamins A, D, E, and K) at bedtime or at least 2 hours apart from orlistat.
• Stop orlistat and seek urgent medical advice if you develop jaundice, dark urine, pale stools, or severe abdominal pain.
• Orlistat may interact with warfarin, ciclosporin, levothyroxine, and other medicines. Tell your prescriber about all medicines you take.

Understanding obesity and its health consequences

Obesity is defined as a BMI of 30 kg/m2 or above.

It results from a chronic imbalance between energy intake and energy expenditure, influenced by genetic predisposition, dietary habits, physical activity levels, psychological factors, socioeconomic status, and the obesogenic environment.

Excess adipose tissue, particularly visceral fat stored around the internal organs, is metabolically active and releases inflammatory cytokines, adipokines, and free fatty acids that contribute to insulin resistance, systemic inflammation, and endothelial dysfunction.

The health consequences of obesity are wide-ranging. Type 2 diabetes risk is 5 to 10 times higher in obese individuals compared with those of healthy weight.

Cardiovascular disease risk, including coronary heart disease and stroke, is substantially elevated. Hypertension affects approximately 40 percent of obese adults. Dyslipidaemia (elevated triglycerides, low HDL cholesterol) is common.

Non-alcoholic fatty liver disease affects up to 70 percent of obese individuals and can progress to cirrhosis.

Obstructive sleep apnoea, gastro-oesophageal reflux disease, osteoarthritis (particularly of the knees and hips), depression, and reduced fertility are all more prevalent.

Obesity increases the risk of several cancers, including breast, colorectal, endometrial, oesophageal, kidney, and pancreatic cancer.

How orlistat works

Dietary fat (triglycerides) cannot be absorbed directly through the intestinal wall. It must first be broken down into smaller molecules (monoglycerides and free fatty acids) by lipase enzymes.

Gastric lipase, produced in the stomach, initiates fat digestion, while pancreatic lipase, secreted into the duodenum, completes the process.

Orlistat binds covalently to the active serine site of these lipases, forming an irreversible (within the timeframe of gut transit) enzyme-inhibitor complex that renders the lipase inactive.

With approximately 30 percent of dietary fat rendered undigestible, the unabsorbed triglycerides pass through the small intestine and colon and are excreted in the faeces.

This creates an energy deficit of approximately 200 to 300 kcal per day (assuming a typical fat intake), contributing to weight loss over time.

The gastrointestinal side effects (oily stools, flatulence with discharge, faecal urgency) are a direct and predictable consequence of this mechanism.

They are more pronounced when dietary fat intake is high, which provides a built-in behavioural feedback mechanism encouraging patients to adhere to a lower-fat diet.

Orlistat acts entirely within the gut lumen. Less than 1 percent of the dose is absorbed systemically, and the absorbed fraction is rapidly metabolised and excreted.

This means that systemic pharmacological effects are negligible, and the drug does not act on the brain, cardiovascular system, or metabolism directly.

Weight loss with orlistat is achieved solely through reduced calorie absorption from fat.

Clinical evidence for orlistat

Orlistat has been evaluated in numerous large randomised controlled trials.

The pivotal European Multicentre Orlistat Study randomly assigned 743 obese adults to orlistat 120 mg three times daily or placebo for 2 years, both groups following a reduced-calorie diet.

After 1 year, the orlistat group lost a mean of 10.2 percent of initial body weight compared with 6.1 percent in the placebo group.

In the second year, weight regain was less in the orlistat group.

Orlistat also produced significant reductions in total cholesterol, LDL cholesterol, blood pressure, and fasting insulin levels, independent of weight loss.

The XENDOS trial (XENical in the Prevention of Diabetes in Obese Subjects) followed 3,305 obese adults over 4 years.

Orlistat plus lifestyle changes reduced the incidence of type 2 diabetes by 37 percent compared with lifestyle changes plus placebo in the overall population.

In the subgroup with impaired glucose tolerance at baseline, the risk reduction was even greater.

Mean weight loss was 5.8 kg with orlistat versus 3.0 kg with placebo over 4 years.

NICE guideline CG189 (Obesity: identification, assessment and management) recommends considering pharmacotherapy, including orlistat, as an adjunct to lifestyle interventions for adults with a BMI of 30 or above, or a BMI of 28 or above with associated risk factors.

Treatment should be reviewed at 12 weeks, and continued only if the patient has lost at least 5 percent of initial body weight.

Orlistat compared with other weight management options

Orlistat is one of a limited number of pharmacological options for weight management in the UK.

Liraglutide 3.0 mg (Saxenda) is a GLP-1 receptor agonist administered as a daily subcutaneous injection, producing greater mean weight loss than orlistat but at higher cost and with injectable administration.

Semaglutide 2.4 mg (Wegovy) is a once-weekly GLP-1 receptor agonist that has demonstrated substantial weight loss in clinical trials. Naltrexone/bupropion (Mysimba) acts on appetite centres in the brain.

Bariatric surgery is the most effective intervention for severe obesity (BMI 40 or above, or BMI 35 or above with comorbidities) and produces sustained long-term weight loss of 20 to 35 percent.

Each option has a different risk-benefit profile, cost, and suitability depending on the individual patient.

Orlistat has the advantage of a well-established safety profile over more than 20 years of use, minimal systemic absorption, no effect on the central nervous system, no cardiovascular stimulant properties, and availability as a generic medicine.

Its main limitation is the modest magnitude of additional weight loss and the gastrointestinal side effects, which some patients find unacceptable.

Dosage and administration

Take one 120 mg capsule of orlistat immediately before, during, or up to one hour after each of three main meals daily.

If a meal is skipped or contains no fat, omit the orlistat dose. Swallow the capsule whole with water.

Follow a nutritionally balanced, reduced-calorie diet providing approximately 30 percent of calories from fat, distributed evenly across three meals.

Take a daily multivitamin supplement at bedtime containing vitamins A, D, E, and K.

Treatment should be reviewed after 12 weeks.

If you have not lost at least 5 percent of your starting body weight, your prescriber will usually recommend stopping orlistat, as further weight loss is unlikely with continued use.

If treatment is effective, it may be continued alongside dietary and exercise programmes for as long as it remains beneficial, with regular reviews.

Side effects of orlistat

Gastrointestinal effects

The most common side effects are oily or fatty stools, oily spotting on underwear, flatulence with oily discharge, increased bowel movements, faecal urgency, and abdominal discomfort.

These effects are directly related to undigested fat passing through the bowel and are more severe when dietary fat intake exceeds 30 percent of total calories.

They tend to improve with dietary adherence and may diminish over several weeks as patients learn to moderate their fat intake.

Nutritional effects

Reduced absorption of fat-soluble vitamins (A, D, E, K) can occur with long-term use. Supplementation is recommended.

Patients who are already deficient in these vitamins or who have conditions affecting vitamin absorption should be monitored.

Vitamin D deficiency is common in the UK population, and orlistat may worsen this.

Rare but serious effects

Hepatic injury has been reported very rarely. Symptoms include jaundice, dark urine, pale stools, and upper abdominal pain. Stop orlistat and seek immediate medical advice if these occur.

Oxalate nephropathy (kidney damage from increased urinary oxalate) has been reported, particularly in patients with pre-existing kidney disease or dehydration. Maintain adequate fluid intake.

Pancreatitis has been reported very rarely. Severe allergic reactions (angioedema, anaphylaxis) are extremely rare.

When to seek medical advice

Stop orlistat and contact your prescriber urgently if you develop yellowing of the skin or eyes, dark urine, pale stools, severe abdominal pain, or persistent nausea.

Seek emergency help by calling 999 if you experience signs of a severe allergic reaction.

Contact your GP or NHS 111 for persistent or distressing gastrointestinal symptoms, rectal bleeding, or signs of vitamin deficiency.

Report suspected adverse reactions to the MHRA at yellowcard.mhra.gov.uk .

Warnings and precautions

Contraindications

Orlistat is contraindicated in chronic malabsorption syndrome, cholestasis, pregnancy, breastfeeding, and hypersensitivity to orlistat or any excipient.

Drug interactions

Orlistat may reduce the absorption of ciclosporin (monitor levels closely), warfarin (monitor INR), levothyroxine (take 4 hours apart, monitor thyroid function), antiepileptic medicines, amiodarone, and antiretroviral medicines.

Oral contraceptive effectiveness may be reduced if severe diarrhoea occurs; use additional contraception. Discuss all medicines with your prescriber before starting orlistat.

Special populations

Patients with type 2 diabetes should be monitored for hypoglycaemia, as weight loss may improve glycaemic control and necessitate dose reductions in diabetes medication.

Patients with chronic kidney disease are at increased risk of oxalate nephropathy. Elderly patients may use orlistat without dose adjustment.

Lifestyle and behavioural support

Orlistat is most effective when used as part of a comprehensive weight management programme.

NICE CG189 recommends a multicomponent approach including dietary modification (reducing overall calorie intake, increasing fruit, vegetable, and fibre intake, and reducing saturated fat and sugar), regular physical activity (at least 150 minutes of moderate-intensity activity per week), and behavioural support (goal setting, self-monitoring, stimulus control, cognitive restructuring).

NHS weight management programmes, practice nurse consultations, dietitian referrals, and digital tools such as the NHS Better Health app can provide structured support.

Psychological therapies, particularly cognitive behavioural therapy, can help address emotional eating, binge eating, and low motivation.

How to get orlistat 120 mg in the UK

Orlistat 120 mg is available on NHS prescription from your GP, weight management clinic, or an authorised online prescriber registered with the General Pharmaceutical Council (GPhC).

The standard NHS prescription charge in England is 9.90 pounds per item; prescriptions are free in Scotland, Wales, and Northern Ireland.

The lower-strength 60 mg formulation (Alli) can be purchased from pharmacies without prescription after a consultation with the pharmacist.

Sources

• Orlistat 120 mg hard capsules, Summary of Product Characteristics (EMC)
• Orlistat, British National Formulary (BNF)
• NICE CG189: Obesity, identification, assessment and management
• Obesity, NHS
• NHS Better Health: Lose weight
• MHRA Yellow Card Scheme