Alli (orlistat 60 mg) is one of the few weight loss pills available over the counter in UK pharmacies, but is Alli a good weight loss pill for you? As a lipase inhibitor, Alli works by blocking the absorption of roughly one-third of dietary fat, supporting gradual weight loss when combined with a calorie-controlled diet and regular physical activity. It is a Pharmacy (P) medicine, meaning a pharmacist must assess your suitability before you can purchase it. This article examines the clinical evidence, who Alli is appropriate for, its side effects, key drug interactions, and how to use it safely and effectively.

What Is Alli and How Does It Work?

Alli is the brand name for orlistat 60 mg, an over-the-counter weight loss capsule available in the UK without a prescription. It is classified as a Pharmacy (P) medicine, meaning it can only be purchased following a brief assessment by a pharmacist, who will confirm it is appropriate for you. It belongs to a class of medicines known as lipase inhibitors. A higher-dose version — orlistat 120 mg, marketed as Xenical — is available on prescription only. Both formulations are licensed in the UK by the Medicines and Healthcare products Regulatory Agency (MHRA); product information including the Summary of Product Characteristics (SmPC) and Patient Information Leaflet (PIL) for both products is available on the Electronic Medicines Compendium (EMC). The European Medicines Agency (EMA) holds the original EU marketing authorisation documentation, but UK patients and clinicians should refer primarily to MHRA-approved labelling and the EMC.

Orlistat works by inhibiting pancreatic and gastric lipases — enzymes in the digestive system responsible for breaking down dietary fat. When these enzymes are blocked, approximately one-third of the fat consumed in a meal cannot be absorbed and is instead excreted in the stool. This reduction in caloric absorption from fat contributes to a calorie deficit, which, when combined with dietary changes and physical activity, can support gradual weight loss.

It is important to understand that Alli is not an appetite suppressant and does not act on the brain or central nervous system. Its mechanism is entirely localised to the gastrointestinal tract. This means it only works in the context of fat consumption — if a meal contains little or no fat, the medicine will have minimal effect. Alli is therefore most effective when used as part of a structured, calorie-controlled diet that includes a moderate fat intake, rather than as a standalone solution.

Clinical Evidence for Alli as a Weight Loss Aid

The clinical evidence supporting orlistat as a weight loss aid is well established. Multiple randomised controlled trials and systematic reviews have demonstrated that orlistat, when combined with a reduced-calorie diet and increased physical activity, produces statistically significant weight loss compared with placebo. Data summarised in the Xenical 120 mg SmPC and in Cochrane reviews indicate that, on average, orlistat 120 mg produces approximately 2.5–3.5 kg more weight loss than placebo over 12 months, with a greater proportion of patients achieving clinically meaningful thresholds of 5% or 10% body weight loss. Individual results vary considerably.

For the 60 mg over-the-counter dose available in Alli, the Alli SmPC and PIL indicate that users may lose more weight than with diet and exercise alone, though the absolute additional benefit at this lower dose is more modest than at 120 mg. These figures represent averages across study populations and should not be taken as a guarantee of individual outcomes.

Longer-term data from the XENDOS trial demonstrated that orlistat 120 mg (prescription strength), combined with lifestyle intervention, reduced the progression from impaired glucose tolerance to type 2 diabetes compared with lifestyle intervention alone. This finding relates specifically to the 120 mg dose; there is limited direct evidence that the OTC 60 mg dose confers the same diabetes-prevention benefit.

The evidence consistently shows that Alli is not a standalone solution — its benefits are modest and depend heavily on sustained lifestyle changes. For the OTC 60 mg formulation, the PIL advises stopping treatment if no weight loss has occurred after 12 weeks, as continued benefit is unlikely. For prescription-strength orlistat 120 mg, the SmPC recommends discontinuation if less than 5% of initial body weight has been lost after 12 weeks. Additionally, Alli 60 mg is intended for use for up to 6 months; if longer-term pharmacotherapy is needed, this should be discussed with a GP or specialist.

Who Is Alli Suitable For in the UK?

In the UK, Alli is available over the counter from pharmacies for adults aged 18 and over with a body mass index (BMI) of 28 kg/m² or above. This threshold is set because the risk-benefit profile of orlistat is considered favourable only when a meaningful degree of excess weight is present. Pharmacists are trained to conduct a brief consultation before supplying Alli to ensure it is appropriate for the individual.

Alli may be particularly suitable for adults who:

• Have a BMI of 28 kg/m² or above and have not achieved sufficient weight loss through diet and exercise alone

• Are motivated to make sustained dietary changes alongside taking the medication

• Do not have contraindications such as chronic malabsorption syndrome or cholestasis

• Are not taking medications that may interact with orlistat (see the side effects and safety section below)

Alli is not suitable for pregnant or breastfeeding women, children under 18, or those with conditions causing fat malabsorption. People with type 2 diabetes, thyroid conditions, renal impairment, or a history of kidney stones should seek GP advice before starting Alli, as weight loss may alter medication requirements and certain conditions increase the risk of adverse effects such as oxalate nephropathy.

NICE guideline CG189 (Obesity: identification, assessment and management) recommends that prescription-strength orlistat 120 mg be considered for adults with a BMI of 30 kg/m² or above, or 28 kg/m² or above in the presence of weight-related risk factors such as type 2 diabetes or hypertension, within a structured weight management programme. If you are considering whether lower BMI thresholds may apply to you based on your ethnic background, discuss this with your GP, who can refer to relevant NICE public health guidance.

Common Side Effects and Safety Considerations

The most frequently reported side effects of Alli are gastrointestinal in nature and are a direct consequence of its mechanism of action. When undigested fat passes through the bowel, it can cause:

• Oily or fatty stools (steatorrhoea)

• Urgent or frequent bowel movements

• Flatulence, sometimes with oily discharge

• Stomach cramps or discomfort

• Faecal incontinence in some cases

These effects are more pronounced when dietary fat intake is high, which is why adhering to a low-fat diet (no more than 30% of calories from fat) is strongly recommended. Many users find that the gastrointestinal side effects serve as a behavioural deterrent to consuming high-fat foods, which can reinforce dietary compliance.

Orlistat can also reduce the absorption of fat-soluble vitamins — specifically vitamins A, D, E, and K. For this reason, it is advisable to take a daily multivitamin supplement containing these nutrients at bedtime, or at least two hours before or after taking Alli, to minimise any interaction.

Rare but serious side effects have been reported, including liver injury and kidney stones (oxalate nephropathy). The MHRA advises that patients experiencing symptoms such as jaundice, dark urine, severe abdominal pain, or rectal bleeding should stop taking orlistat and seek urgent medical attention. Signs of a serious allergic reaction — such as swelling of the face, lips, or throat, or difficulty breathing — also require immediate medical attention. Suspected side effects should be reported to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

Drug interactions are an important safety consideration:

• Ciclosporin: Orlistat is contraindicated with ciclosporin when purchased OTC; concomitant use can significantly reduce ciclosporin blood levels.

• Warfarin and other anticoagulants: Orlistat may affect vitamin K absorption and alter anticoagulation control; INR should be monitored more closely.

• Levothyroxine: Separate administration by at least four hours to avoid reduced absorption; monitor thyroid function.

• Acarbose: Concomitant use is not recommended.

• Amiodarone: Orlistat may reduce amiodarone levels; monitoring is advised.

• Antiepileptic drugs: Orlistat may alter seizure control; monitor carefully.

• Antiretroviral drugs (ART): Orlistat may reduce absorption of some antiretroviral medicines; seek specialist advice.

• Oral contraceptives: If severe diarrhoea occurs, the absorption of oral contraceptives may be reduced. Use additional contraceptive precautions (such as condoms) during and for seven days after any episode of severe diarrhoea.

Always inform your pharmacist or GP of all current medications before starting Alli.

Guidance on Using Alli Safely and Effectively

To maximise the benefits of Alli and minimise side effects, it should be taken as directed — one 60 mg capsule with each main meal containing fat, up to three times daily. It can be taken immediately before, during, or up to one hour after a meal. If a meal is skipped or contains no fat, the dose should be omitted. Alli should not be taken with snacks. Taking more than the recommended dose does not increase weight loss and significantly raises the risk of gastrointestinal side effects.

Alli 60 mg is intended for use for up to 6 months. If you feel you need weight loss support beyond this period, speak to your GP about longer-term options within a structured weight management programme.

Dietary preparation is essential before starting Alli. The NHS and MHRA recommend adopting a balanced, calorie-controlled diet in which no more than 30% of daily calories come from fat, spread evenly across meals. As a rough guide, this equates to approximately 12–19 g of fat per main meal, depending on your individual daily calorie target. Keeping a food diary can help you monitor fat consumption and identify patterns that may be contributing to side effects or limiting weight loss progress.

Take your daily multivitamin at bedtime or at least two hours before or after your Alli dose. If you take levothyroxine, separate it from Alli by at least four hours.

Regular physical activity should accompany Alli use. Even modest increases in activity — such as 30 minutes of brisk walking five days a week — can meaningfully enhance weight loss outcomes. Users should set realistic expectations: a loss of 0.5–1 kg per week is considered a safe and sustainable rate.

When to seek medical advice:

• If you have not lost any weight after 12 weeks of taking Alli 60 mg

• If you experience severe or persistent abdominal pain, jaundice, dark urine, or rectal bleeding

• If you are taking prescription medications that may interact with orlistat

• If you develop symptoms that may suggest vitamin deficiency, such as fatigue, bone pain, or easy bruising

• If you wish to continue weight loss pharmacotherapy beyond 6 months

Alli can be a useful adjunct to lifestyle changes for eligible adults, but it is not a substitute for long-term behavioural modification. For those with significant obesity or complex health needs, referral to a GP or specialist weight management service is strongly encouraged. Further information is available on the NHS website and in the Patient Information Leaflet supplied with Alli.

Frequently Asked Questions