Contrave after gastric sleeve surgery is a question increasingly raised by patients experiencing weight regain or a plateau following their procedure. In the UK, the equivalent authorised medicine is Mysimba (naltrexone/bupropion prolonged-release tablets); Contrave is the US brand name and is not a licensed UK product. While some patients may meet the standard criteria for Mysimba, its use in the post-bariatric population is not explicitly studied in clinical trials, and altered gastric physiology following sleeve gastrectomy can affect how the medicine is absorbed. Any decision to use weight management medication after bariatric surgery must involve your specialist bariatric team.

What Is Naltrexone/Bupropion (Mysimba) and How Does It Work for Weight Management

Mysimba (naltrexone/bupropion) is a centrally acting prescription medicine licensed in the UK for chronic weight management in adults with a BMI of 30 kg/m² or above, working by stimulating hypothalamic appetite-regulating neurones and blocking their autoinhibitory feedback loop.

In the United Kingdom and European Union, the combination of naltrexone and bupropion is authorised as a prescription medicine under the brand name Mysimba (naltrexone/bupropion 8 mg/90 mg prolonged-release tablets). The US brand name Contrave refers to the same active ingredients but is not the authorised UK product. Current NHS commissioning of Mysimba is limited, and NICE has not recommended it for routine NHS use; patients should discuss availability with their specialist.

Mysimba is indicated as an adjunct to a reduced-calorie diet and increased physical activity for chronic weight management in adults with an initial BMI of 30 kg/m² or greater, or 27 kg/m² or greater in the presence of at least one weight-related comorbidity (such as type 2 diabetes, dyslipidaemia, or hypertension).

The two active ingredients work on distinct but complementary pathways in the brain:

• Bupropion is a dopamine and noradrenaline reuptake inhibitor that stimulates pro-opiomelanocortin (POMC) neurones in the hypothalamus, which are involved in appetite regulation and energy expenditure. In the UK, bupropion is separately licensed as Zyban for smoking cessation; it does not hold a UK licence for depression.

• Naltrexone is an opioid receptor antagonist that blocks the autoinhibitory feedback loop on POMC neurones, thereby sustaining and amplifying bupropion's appetite-suppressing effect. Naltrexone is separately licensed in the UK for alcohol and opioid dependence.

Together, these agents act centrally to reduce hunger and food cravings, particularly for highly palatable foods. Clinical trials have demonstrated modest but meaningful weight loss when used alongside lifestyle modification. The combination carries a range of potential side effects and contraindications, and its use must always be supervised by a qualified healthcare professional within a comprehensive weight management programme.

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Using Mysimba After Gastric Sleeve Surgery: Key Considerations

There is no specific licensed indication for Mysimba in the post-bariatric population; use must be agreed collaboratively with the bariatric MDT, with documented informed consent and individual assessment of BMI criteria, contraindications, and clinical readiness.

Sleeve gastrectomy, commonly known as gastric sleeve surgery, is one of the most frequently performed bariatric procedures in the UK. It involves removing approximately 75–80% of the stomach, creating a narrow, sleeve-shaped pouch. While many patients achieve significant and sustained weight loss, some experience weight regain over time — a phenomenon that can prompt consideration of adjunctive pharmacological support.

Using Mysimba after gastric sleeve surgery raises several important clinical considerations. There is no specific licensed indication for naltrexone/bupropion in the post-bariatric surgery population. If a patient meets the standard SmPC BMI and comorbidity criteria, use of Mysimba may still fall within the licensed indication; however, post-bariatric use is not explicitly studied in the authorised clinical trial programme, and robust data in this specific population remain limited. Importing or using the US brand Contrave in the UK would constitute use of an unlicensed medicine. Any decision to use such medication post-operatively should be made collaboratively between the patient and their bariatric multidisciplinary team (MDT), with explicit informed consent and documented clinical rationale.

Key considerations include:

• Timing: Most bariatric services consider pharmacotherapy after weight has stabilised or plateaued, typically following the period of maximal post-operative weight loss. There is no fixed UK-mandated interval; the bariatric MDT will assess readiness on an individual basis in line with NHS England Tier 4 service expectations and BOMSS guidance.

• Indication: Medication may be considered if weight regain is clinically significant or if weight loss has plateaued despite adherence to dietary and lifestyle recommendations.

• Contraindications: These include uncontrolled hypertension, a history of seizures or conditions that lower the seizure threshold, current or recent eating disorders (anorexia nervosa or bulimia nervosa), severe hepatic impairment, end-stage renal disease, pregnancy or breastfeeding, acute opioid withdrawal, and abrupt discontinuation of alcohol or benzodiazepines. Bupropion is also contraindicated in patients taking monoamine oxidase inhibitors (MAOIs). Naltrexone is contraindicated in patients requiring opioid-based analgesia.

Patients should never self-prescribe or obtain prescription medicines without medical oversight, particularly given the altered physiology following bariatric surgery.

How Gastric Sleeve Surgery Affects Drug Absorption

Sleeve gastrectomy accelerates gastric emptying and alters gastrointestinal transit, making absorption of Mysimba's prolonged-release formulation unpredictable; the small intestinal surface is preserved, but plasma levels may still be inconsistent.

Understanding how gastric sleeve surgery alters pharmacokinetics is essential when considering any oral medication post-operatively. Sleeve gastrectomy is primarily a restrictive procedure — it significantly reduces gastric volume and accelerates gastric emptying, but does not involve intestinal bypass or rerouting. This distinction is important: the small intestinal absorptive surface area is largely preserved, unlike in Roux-en-Y gastric bypass.

Nevertheless, the changes in gastric volume, pH, and transit time can meaningfully affect how drugs are absorbed:

• Modified-release (prolonged-release) formulations, such as the Mysimba tablet, rely on controlled drug release over time. Accelerated gastric emptying and altered gastrointestinal transit can make absorption of prolonged-release formulations unpredictable — plasma levels may be higher or lower than expected, and the therapeutic effect may be inconsistent.

• Altered gastric pH: Reduced gastric acid production following sleeve gastrectomy may affect the dissolution of certain tablet formulations.

• Changes in body composition: Significant reductions in fat mass and lean body mass alter the volume of distribution for many medicines.

Because of these unpredictable pharmacokinetic effects, the Mysimba prolonged-release tablet must not be crushed, chewed, or split, as this would destroy the modified-release mechanism and risk rapid drug release with increased adverse effects. If absorption is a clinical concern, the bariatric MDT and pharmacist should be consulted regarding alternative agents or formulations.

Routine therapeutic drug monitoring (TDM) is not standard UK practice for naltrexone or bupropion. Instead, close clinical monitoring of weight response, blood pressure, heart rate, and adverse effects — in line with SmPC and Specialist Pharmacy Service (SPS) guidance on medicines use after bariatric surgery — is the recommended approach.

Risks, Side Effects, and Safety Monitoring Post-Surgery

Common side effects of Mysimba include nausea, vomiting, raised blood pressure, and neuropsychiatric symptoms; post-bariatric patients require baseline and ongoing monitoring of blood pressure, mood, weight, and nutritional status.

The combination of naltrexone and bupropion carries a recognised side effect profile that may be particularly relevant in the post-bariatric surgery context, where patients are already navigating significant physiological and nutritional changes.

Common side effects include:

• Nausea, vomiting, and constipation

• Headache and dizziness

• Insomnia and dry mouth

• Increased blood pressure and heart rate

Nausea is among the most frequently reported side effects and can be especially problematic for gastric sleeve patients, who may already experience post-operative nausea or food intolerances. Vomiting in this population carries additional risks, including dehydration and electrolyte imbalance.

Important safety concerns include:

• Neuropsychiatric effects: The Mysimba SmPC includes warnings regarding the risk of neuropsychiatric symptoms, including depressed mood, agitation, and suicidal ideation. Patients with a history of depression or anxiety should be monitored closely, and any new or worsening symptoms should prompt urgent review.

• Seizure risk: Bupropion lowers the seizure threshold in a dose-dependent manner. This risk is heightened in patients with eating disorders, those significantly restricting caloric intake, or those with other seizure risk factors — all of which may be relevant in the post-bariatric context.

• Cardiovascular effects: The combination can raise blood pressure and heart rate. Mysimba is contraindicated in patients with uncontrolled hypertension; blood pressure and heart rate should be measured at baseline and monitored regularly during treatment.

• Hepatic effects: Naltrexone has been associated with hepatocellular injury at higher doses. Liver function tests (LFTs) should be considered at baseline and periodically where clinically indicated, particularly in patients with pre-existing hepatic risk factors.

• Drug interactions: Bupropion is a strong inhibitor of CYP2D6 and can significantly increase plasma concentrations of medicines metabolised by this enzyme, including certain antidepressants, antipsychotics, and beta-blockers. A full medicines reconciliation should be performed before initiating treatment.

Post-bariatric patients are also at risk of nutritional deficiencies (including B vitamins, iron, and vitamin D). Any pre-existing deficiencies should be identified and corrected before initiating treatment, as these may compound neurological and haematological risks.

Recommended monitoring includes: baseline and periodic blood pressure and heart rate; mood and suicidality assessment; weight and waist circumference; and laboratory tests guided by clinical status and nutritional risk.

Patients and carers should be advised to report any suspected adverse reactions via the MHRA Yellow Card Scheme (available at yellowcard.mhra.gov.uk or via the Yellow Card app).

NICE and NHS Guidance on Medication After Bariatric Surgery

NICE has not recommended Mysimba for routine NHS use; post-bariatric pharmacotherapy should be overseen by NHS England Tier 4 bariatric services, with any off-label or unlicensed prescribing requiring explicit informed consent and specialist justification.

In the UK, the use of weight management medicines is governed by guidance from the National Institute for Health and Care Excellence (NICE). NICE Clinical Guideline CG189 (Obesity: identification, assessment and management) provides the core framework for pharmacological intervention, specifying that weight loss medicines should only be initiated and supervised by a specialist as part of a comprehensive programme that includes dietary, physical activity, and behavioural components.

The pharmacological landscape for obesity management in the UK has expanded in recent years:

• Orlistat holds a full UK marketing authorisation and has long been available on the NHS for eligible patients.

• Liraglutide (Saxenda) holds a UK marketing authorisation and has NICE technology appraisal guidance (NICE TA664) supporting its use in specific circumstances.

• Semaglutide (Wegovy) has received MHRA authorisation and NICE technology appraisal guidance (NICE TA875) recommending its use within a specialist weight management service for eligible adults.

• Naltrexone/bupropion (Mysimba) holds a UK/EU marketing authorisation but has not been recommended by NICE for routine NHS use. NHS commissioning of Mysimba is therefore limited, and its availability may vary by region.

With respect to post-bariatric care, NHS England's Tier 4 bariatric services are expected to provide long-term follow-up, including assessment of weight regain and consideration of adjunctive therapies. Key NHS and BOMSS recommendations include:

• Lifelong nutritional supplementation and monitoring

• Annual review by a bariatric MDT

• Psychological support as needed

• Consideration of revisional surgery or pharmacotherapy only after thorough assessment

If Mysimba is prescribed within its licensed indication criteria, this constitutes on-label use. Use of the US brand Contrave, or use outside the SmPC criteria, would constitute unlicensed or off-label prescribing respectively, requiring explicit informed consent, documented clinical rationale, and close specialist oversight in line with GMC Good Practice in Prescribing and Managing Medicines and Devices guidance.

When to Speak to Your Specialist About Weight Loss Medication

Patients should contact their bariatric specialist if they experience significant weight regain, persistent hunger unmanageable by diet alone, or worsening obesity-related comorbidities, rather than seeking prescription medication independently.

If you have undergone gastric sleeve surgery and are concerned about weight regain or a plateau in your weight loss journey, it is important to raise this with your bariatric team rather than seeking medication independently. Self-prescribing or obtaining prescription medicines without medical supervision is unsafe and potentially harmful, particularly given the altered physiology following surgery.

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Contact your GP or bariatric specialist if you notice:

• Significant weight regain — commonly discussed in clinical practice as regaining more than 10–15% of your lowest post-operative weight, though your bariatric MDT will assess this individually

• Persistent hunger or food cravings that are difficult to manage with dietary strategies alone

• Signs of nutritional deficiency, such as fatigue, hair loss, or tingling in the extremities

• Worsening of obesity-related conditions such as type 2 diabetes, hypertension, or sleep apnoea

Seek urgent medical attention on the same day if you experience:

• Persistent vomiting or an inability to keep fluids down

• Severe abdominal pain

• Signs of dehydration (such as dark urine, dizziness, or confusion)

Your specialist may explore a range of options before considering pharmacotherapy, including dietary review, psychological support, increased physical activity, or revisional bariatric procedures. If medication is deemed appropriate, they will assess your full medical history, current medicines, and nutritional status before making any prescribing decision. It is important to bring a complete and up-to-date list of all your medicines to any appointment, as bupropion inhibits the CYP2D6 enzyme and can interact with a number of commonly prescribed medicines, including certain antidepressants, antipsychotics, and beta-blockers.

It is also worth discussing any mental health concerns openly with your team, as both obesity and bariatric surgery can have significant psychological dimensions, and medicines such as bupropion carry neuropsychiatric cautions that require careful consideration.

Ultimately, the most effective and safest approach to long-term weight management after gastric sleeve surgery is one that is personalised, multidisciplinary, and evidence-based — with any pharmacological support forming just one part of a broader, sustained lifestyle strategy.

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