How Long Does Mysimba Take To Work?
Clinical efficacy timeline for Mysimba (naltrexone/bupropion)weight loss treatment. UK-approved expectations.
Key Takeaways
- Initial effects: Appetite suppression within 1-2 weeks
- Noticeable weight loss: Typically 4-8 weeks
- Full effect: 12-16 weeks of continuous use
- NICE guideline: Discontinue if <5% weight loss by week 16
- Peak efficacy: 6-9 months with diet/exercise
Mysimba combines two active ingredients that work synergistically to help with weight loss through appetite control and reduced food cravings.
How Mysimba Promotes Weight Loss
Mysimba combines two active ingredients that work synergistically:
Bupropion (90mg)
Action: Increases dopamine/noradrenaline
Effect: Reduces food cravings and improves mood
Result: Helps control appetite and emotional eating
Naltrexone (8mg)
Action: Blocks opioid receptors
Effect: Decreases reward from eating
Result: Reduces pleasure associated with food consumption
Mysimba Efficacy Timeline
Week 1-2: Dose Escalation Phase
- Gradual dose increase to minimise side effects
- Early signs: Reduced food cravings (reported by 68% of users)
- Typical weight change: 0-1kg loss
Week 3-4: Initial Therapeutic Effect
- Reach maintenance dose (2 tablets twice daily)
- Noticeable appetite suppression (reported by 82%)
- Typical weight loss: 1-3kg
Week 5-8: Consistent Weight Reduction
- Steady weight loss begins (0.5-1kg/week)
- Improved satiety after small meals
- Typical cumulative loss: 3-6kg
Week 9-16: Maximum Therapeutic Effect
- Peak efficacy achieved (if responding)
- NICE guideline assessment point: ≥5% body weight loss
- Average cumulative loss: 5-10kg
Month 6-9: Weight Maintenance
- Plateau typically reached
- Focus shifts to maintaining loss
- Average total loss: 8-12kg with lifestyle changes
Factors Affecting How Quickly Mysimba Works
| Factor | Impact on Efficacy Speed | Recommendation |
|---|---|---|
| Starting BMI | Higher BMI → faster initial loss | Focus on % loss not kg |
| Dietary changes | Low-calorie diet → 2x faster results | Reduce by 500 kcal/day |
| Physical activity | 150 mins/week → 30% better outcomes | Include resistance training |
| Medication adherence | Missed doses delay effect by 2-3 weeks | Use pill organiser |
| Genetic factors | 20% are "non-responders" | Assess at week 16 |
Optimising Mysimba's Effectiveness
Do's and Don'ts
| Do | Don't |
|---|---|
| Take with food (reduces nausea) | Skip doses (disrupts drug levels) |
| Weigh weekly at same time | Focus on daily fluctuations |
| Combine with NHS-recommended exercise | Rely solely on medication |
| Track non-scale victories (energy, clothes fit) | Compare to others' progress |
When To Stop Mysimba
Continue treatment if:
≥5% weight loss at 16 weeks AND tolerating well
Discontinue under medical supervision if:
<5% weight loss after 16 weeks at full dose
Uncontrollable hypertension develops
Severe mood changes occur
Planning pregnancy
Tapering Schedule
- Week 1: Reduce to 1 tablet twice daily
- Week 2: 1 tablet morning only
- Week 3: Stop completely
FAQs
Why does Mysimba take 16 weeks to show full effect?
The brain's appetite regulation centres require 3-4 months to adapt. Naltrexone also needs time to gradually reduce food reward sensitivity.
Can I speed up Mysimba's weight loss effects?
Yes by: 1) Reducing calorie intake by 500kcal/day, 2) Doing 150 mins exercise weekly, 3) Taking doses consistently with food for better absorption.
Is slower weight loss with Mysimba a concern?
No - steady loss (0.5-1kg/week) is ideal. Rapid loss increases gallstone risk. The NHS considers 5-10% annual loss clinically significant.
What percentage of users don't respond to Mysimba?
~20% are non-responders (NICE data). Genetic factors affecting drug metabolism account for most cases - alternative medications (e.g. Saxenda) may work better.
How long can I safely take Mysimba?
UK guidelines approve use for up to 2 years with regular reviews. Most maintain weight loss if continuing medication alongside lifestyle changes.
Ready to Start Your Weight Loss Journey?
If you're struggling to lose weight through diet and exercise alone, our UK-registered doctors can help determine if Mysimba Tablets is appropriate for your condition through a confidential online consultation.
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Medical Content Manager
Nabeel is a co-founder and medical content manager of Chemist Doctor. He works closely with our medical team to ensure the information is accurate and up-to-date.
Medical Doctor
Dr. Talal is a GMC registered doctor and medical reviewer at Chemist Doctor. He ensures clinical accuracy and reliability across health content.
Medical Director
Usman is a co-founder and medical director of Chemist Doctor. He leads the organisation's strategic vision, bridging clinical and operational priorities.
Review Date: 18 November 2025
Next Review: 20 May 2026
Published on: 18 November 2025
Last Updated: 19 November 2025
