Mounjaro vs Wegovy vs Alli: Which Is Right for You?

In this guide

Mounjaro vs Wegovy vs Alli: Which Is Right for You?

With weight loss still a trending topic online (terms like "best weight loss", "lose weight fast", "weight loss guide" continue to rise), understanding your options has never been more important. In this article, we compare three popular choices:

  • Mounjaro (tirzepatide) — weekly injection
  • Wegovy (semaglutide) — weekly injection
  • Alli (orlistat) — daily oral capsules

We break down licence criteria, how they work, key differences—especially how Alli avoids injections—and the side-effect profiles.

BMI Eligibility – Who Can Take Them?

Medication Licence BMI Threshold Injection?
Mounjaro ≥30 kg/m², or ≥27 kg/m² with a weight-related condition (e.g. hypertension, pre-diabetes) ✅ Weekly injection
Wegovy ≥30 kg/m², or ≥27 kg/m² with weight-related conditions (lower BMI threshold for some ethnic groups) ✅ Weekly injection
Alli BMI ≥28 kg/m² for adults 18+ ❌ Oral capsule

All alongside reduced-calorie diet and exercise.

Key difference: Mounjaro and Wegovy require injections and are prescription-only, while Alli is a non-invasive, pharmacy-available capsule—no injection needed.

How They Work

  • Mounjaro: GIP/GLP-1 dual agonist—slows stomach emptying, reduces appetite, enhances satiety
  • Wegovy: GLP-1 agonist—tricks the brain into feeling full, curbing appetite
  • Alli: Orlistat blocks about 25–30% of fat absorption through lipase inhibition, passing unabsorbed fat in stools

Weight Loss Results

  • Mounjaro: ~20% body weight reduction (~5 stone for 18 stone individual)
  • Wegovy: ~14% body weight reduction in comparable trials
  • Alli: Modest additional weight loss—around 3–5% extra beyond diet & exercise

Side Effects Comparison

Side Effect Mounjaro / Wegovy (GLP-1 injections) Alli (Orlistat capsules)
Nausea ✓ Very common (~30–75%) Rare
Vomiting/Diarrhea ✓ Common (10–15%) ✓ Common (diarrhea ~15%)
Constipation ✓ (~10–15%) ✓ (~5%)
GI discomfort (bloating, cramps) ✓ (~5–15%) ✓ (~5–10%), oily stools
Injection-site reactions ✓ Common —
Pancreatitis (serious) ⚠️ Rare cases reported Rare
Fat-soluble vitamin deficiency — ⚠️ Possible, requires multivitamin A, D, E, K
Severe allergic reactions Rare Rare but serious
Rectal bleeding, gallstones, hepatitis, kidney stones Rare Possible, seek medical advice

How to Take Alli

  • Take one capsule three times a day.
  • Take immediately before, during or up to one hour after a meal containing fat.
  • Skip the dose if a meal is missed or contains no fat.
  • Do not exceed 3 capsules daily.
  • Follow a reduced-calorie, lower-fat diet to minimize side effects.
  • Use for a maximum of six months.
  • If no weight loss occurs after 12 weeks, consult your doctor or pharmacist to reassess treatment.
  • Physical activity should be part of your weight loss plan.

Warnings and Precautions for Alli

Do not take Alli if you:

  • Are pregnant or breastfeeding
  • Have chronic malabsorption syndrome or cholestasis
  • Are taking ciclosporin or warfarin (unless supervised)
  • Have certain kidney problems

Use caution if you:

  • Have diabetes, kidney disease, epilepsy, thyroid disorders, HIV, heart rhythm problems, or take medicines for psychiatric disorders
  • Use hormonal contraceptives (consider extra contraception if severe diarrhoea occurs)
  • Take medicines for high blood pressure or cholesterol

Important: Take a multivitamin containing vitamins A, D, E, and K at bedtime while using Alli.

Because Alli can reduce the absorption of fat-soluble vitamins, it is recommended that you take a daily multivitamin containing vitamins A, D, E and K. You can explore a range of suitable multivitamin options at Weldricks:

Centrum Advance Multivitamins

Lamberts A-Z Multivitamins & Minerals Tablets Pack of 60

View all Vitamins and Supplements

Taking your multivitamin at bedtime, when you are not taking Alli, helps ensure better vitamin absorption.

Why Choose Injection-Free Alli?

  • No needles: ideal for those avoiding injections.
  • Over-the-counter convenience: available directly from Weldricks.
  • Targets fat absorption, not appetite—works differently.
  • Best suited for mild-weight-loss goals and supplementing lifestyle change.

Expert Advice

  • GLP-1 injections produce significantly greater weight loss (14–20%) but demand medical supervision due to side effects and injection use.
  • Alli offers a lower-risk, simpler route—no prescription or injection, but more modest results (3–5%).
  • Choosing depends on BMI eligibility, risk tolerance, cost, and willingness to self-inject.

FAQs

Can I take Alli and Wegovy together?

Currently, no studies support combining GLP-1 medications with orlistat (Alli). Always consult a healthcare professional.

Is Alli as effective as Wegovy or Mounjaro?

No—Alli offers more modest weight loss (3–5%), while GLP-1s like Wegovy/Mounjaro may deliver 14–20% reductions.

Is Alli available over the counter?

Yes. Alli 60mg is available without prescription for adults aged 18+, directly from Weldricks.

Who shouldn’t take Alli?

Anyone with chronic malabsorption syndromes, cholestasis, certain medication interactions, pregnancy, or breastfeeding. Consult your pharmacist.

Where to Buy

Bottom Line

  • Mounjaro and Wegovy are powerful prescription options (BMI ≥27/30), delivering dramatic weight loss—but require injections and can cause significant side effects.
  • Alli offers a gentle, OTC approach: no injections, fewer systemic side effects, but less dramatic results.

Alli is a sensible gateway for those seeking non-invasive weight loss, while GLP-1 drugs are best suited to individuals needing deeper medical intervention.

Written by Allan Green, Pharmacist & Health Writer — bringing you trusted insights and practical choices for smarter weight management.

FAQs

What is the difference between Mounjaro, Wegovy and Alli?

Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections designed for people with a BMI ≥27–30. Alli (orlistat) is an over-the-counter oral capsule available without prescription for BMI ≥28. Mounjaro and Wegovy work by regulating appetite hormones, while Alli works by blocking fat absorption.

Which weight loss medication is most effective?

Mounjaro is currently showing the highest weight loss in clinical trials (~20% body weight reduction), followed by Wegovy (~14%). Alli offers modest extra weight loss of 3–5% when combined with diet and exercise.

Is Alli safer than Mounjaro or Wegovy?

Alli generally has fewer systemic side effects since it works locally in the gut, but can cause gastrointestinal issues like oily stools. Mounjaro and Wegovy may cause nausea, vomiting, and in rare cases, pancreatitis or gallstones. All treatments should be used under professional advice.

Can I take Alli if I don’t want injections?

Yes. Alli is ideal for those who want to avoid injections. It’s available over-the-counter for adults aged 18+ with a BMI of 28 or higher and works alongside diet and exercise.

Do I need a prescription for Alli?

No. Alli 60mg capsules can be purchased without a prescription in the UK from pharmacies like Weldricks, provided you meet the BMI and suitability criteria.

How long should I take Alli for weight loss?

Alli is licensed for up to 6 months of use. If you haven’t lost weight after 12 weeks, you should stop and speak to a pharmacist or doctor for further advice.

Can I combine Alli with Wegovy or Mounjaro?

Currently, there’s no clinical evidence supporting combining GLP-1 medications like Wegovy or Mounjaro with Alli. Always consult a healthcare professional before combining treatments.

What are the side effects of Alli capsules?

Common side effects include oily stools, flatulence, urgent bowel movements, and abdominal pain. Following a lower-fat diet helps minimise these effects.

What BMI do I need for Mounjaro, Wegovy and Alli?

  • Mounjaro: BMI ≥30, or ≥27 with weight-related conditions.
  • Wegovy: BMI ≥30, or ≥27 with weight-related conditions.
  • Alli: BMI ≥28.

Does Alli affect vitamin levels?

Yes. Alli may reduce absorption of fat-soluble vitamins (A, D, E, K). Taking a multivitamin daily while using Alli is recommended.

Published 9th June 2025 by

Allan Green

Allan Green

Registered Pharmacist & Head of E-commerce

Allan has been a Registered Pharmacist for 25+ years

He specializes in Ecommerce and Over the Counter medicines.

He is a Registered Pharmacist, who studied at University of Bradford.

He has been with Weldricks since 2006, starting as a branch manager before moving into area management and deputy superintendent roles.

His current responsibilities include web development, marketing, content, customer service and web operations teams.

GPhC Registration: 2049602