Weight Loss Injections vs Tablets: Which Should You Choose?

When people think about weight loss medication, most attention goes to GLP-1 injections like Mounjaro and Wegovy. But there are also tablet options — Orlistat (Alli/Xenical) and Mysimba — that take completely different approaches. This guide compares the two categories to help you understand which might be appropriate for your situation.

The fundamental differences

Injections and tablets don't just differ in how you take them — they work through entirely different biological mechanisms:

GLP-1 injections (Mounjaro, Wegovy, Saxenda) mimic gut hormones to suppress appetite at the brain level, slow gastric emptying, and improve insulin response. They fundamentally change how hungry you feel.¹²

Orlistat blocks an enzyme (lipase) in your gut that breaks down dietary fat. About 30% of the fat you eat passes through unabsorbed. It doesn't affect appetite — it physically prevents some calories from being absorbed.³

Mysimba combines naltrexone (an opioid antagonist) and bupropion (an antidepressant) to act on the brain's appetite and reward centres. It targets cravings and emotional eating rather than physical hunger or fat absorption.⁴

At a glance

	Injections (GLP-1s)	Orlistat (Alli)	Mysimba
How taken	Weekly or daily injection	Capsule with meals (up to 3×/day)	Tablet twice daily
Mechanism	Appetite suppression via gut hormones	Blocks fat absorption in gut	Acts on brain reward/appetite centres
Avg. weight loss	8–22% (varies by drug)	Up to 5%	Up to 5–8%
Prescription needed?	Yes (all)	No (Alli 60mg is OTC)	Yes
Monthly cost	£150–£299	£20–£50 (OTC)	£70–£100
Common side effects	Nausea, diarrhoea, constipation	Oily stools, flatulence, urgency	Nausea, constipation, insomnia
Key advantage	Most effective option available	Cheapest, no prescription needed	Targets cravings/emotional eating

Effectiveness: the numbers tell the story

The weight loss difference is stark. At maximum doses over approximately 12–18 months:

Mounjaro: up to 22.5%⁵
Wegovy: up to 20.7%⁶
Saxenda: up to 8%⁷
Mysimba: up to 5–8%⁸
Orlistat: up to 5%³

For a person starting at 100kg, that's the difference between losing roughly 20–22kg on Mounjaro versus 5kg on orlistat. Both are clinically meaningful, but they're in different leagues.

Cost: the other side of the equation

Where tablets have a clear advantage is affordability. Alli (orlistat 60mg) costs £20–£50 per month and requires no prescription. Mysimba is £70–£100 per month. Compare that to £189–£299 per month for the GLP-1 injections. Over a year, the difference can be over £2,000.

For many people in the UK, cost is the deciding factor. If you can't afford £200+ per month, the injections simply aren't an option regardless of their superior efficacy. In that case, orlistat or Mysimba combined with diet and exercise changes can still produce meaningful health improvements.

Side effects: very different profiles

The side effects reflect the different mechanisms:

GLP-1 injections primarily cause nausea, vomiting, diarrhoea, and constipation — because slowing gastric emptying affects the whole digestive system. These usually improve after the first few weeks of treatment or after dose increases settle.

Orlistat causes oily stools, flatulence with oily discharge, and urgent bowel movements — because unabsorbed fat has to go somewhere. These side effects are directly proportional to how much fat you eat. Follow a low-fat diet and they're minimal; eat a high-fat meal and you'll know about it. It's essentially built-in behavioural feedback.³

Mysimba causes nausea, constipation, headache, insomnia, and dry mouth. More seriously, it carries a seizure risk (contraindicated in people with seizure history) and can increase blood pressure. The bupropion component also carries rare psychiatric risks.⁴

Accessibility

Orlistat is the most accessible weight loss medication in the UK. Alli (60mg) is available from any pharmacy without a prescription — you just need to speak to the pharmacist. This makes it the only weight loss medication you can start today without a GP appointment or private consultation.

Mysimba requires a prescription but is available on the NHS through specialist services and from private prescribers.

GLP-1 injections all require prescriptions, and NHS access is limited. Most people access them through private prescribers at significant monthly cost.

Who should consider what?

GLP-1 injections are the strongest option if you have a significant amount of weight to lose (BMI 30+), can afford the monthly cost, are comfortable with self-injection, and want the most effective medical support available.

Orlistat makes sense if you're looking for an affordable, accessible first step, prefer tablets over injections, eat a diet that's relatively high in fat (since that's where it makes the biggest difference), or want something you can start immediately without a prescription.

Mysimba may be particularly suitable if your eating patterns are driven by cravings or emotional eating rather than physical hunger, if you can't tolerate GLP-1 medications, or if you prefer a tablet over an injection and want more weight loss than orlistat alone typically provides.

Combining approaches: Some clinicians prescribe combinations in specific cases — for example, a GLP-1 injection alongside Mysimba for enhanced effect — but this should only be done under specialist supervision and is not standard practice.

Regardless of which option you choose, all weight loss medications work best when combined with dietary changes and increased physical activity. No medication is a substitute for lifestyle changes — they're tools that make those changes easier to sustain.

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