Contrave after bariatric surgery is a topic of growing clinical interest as more patients seek pharmacological support for weight regain following procedures such as Roux-en-Y gastric bypass or sleeve gastrectomy. In the UK, Contrave is not available by that name; the equivalent formulation — naltrexone/bupropion prolonged-release tablets — is licensed as Mysimba. Using Mysimba after bariatric surgery raises important questions around altered drug absorption, safety monitoring, and suitability. This article outlines the key clinical considerations, pharmacokinetic implications, and current UK guidance to help patients and clinicians make informed, specialist-led decisions.

What Is Contrave and How Does It Work?

Contrave is not available in the UK; the equivalent medicine is Mysimba (naltrexone/bupropion prolonged-release tablets), licensed by the EMA for weight management in adults with BMI ≥30 kg/m², or ≥27 kg/m² with a weight-related comorbidity.

Contrave is a brand name used in the United States for a combination prescription medication containing two active ingredients: naltrexone and bupropion. This brand name is not used in the United Kingdom. In the UK and across the European Union, the same formulation is marketed as Mysimba (naltrexone/bupropion prolonged-release tablets). Patients and clinicians in the UK should refer to it as Mysimba.

Mysimba is licensed by the European Medicines Agency (EMA) as an adjunct to a reduced-calorie diet and increased physical activity for the management of weight in adults with an initial BMI of 30 kg/m² or above, or 27 kg/m² or above in the presence of at least one weight-related comorbidity (such as type 2 diabetes, dyslipidaemia, or hypertension). Availability on the NHS varies by integrated care board (ICB); patients should check their local formulary. There is currently no NICE technology appraisal recommending routine NHS commissioning of naltrexone/bupropion. For context, NICE has appraised other pharmacological options including semaglutide (TA875) and liraglutide (TA664).

The two components work synergistically on the central nervous system to reduce appetite and food cravings:

• Bupropion is a dopamine and noradrenaline reuptake inhibitor that activates pro-opiomelanocortin (POMC) neurones in the hypothalamus, promoting satiety signals.

• Naltrexone is an opioid receptor antagonist that blocks the auto-inhibitory feedback loop on POMC neurones, thereby sustaining and amplifying bupropion's appetite-suppressing effect.

Together, these mechanisms help reduce caloric intake by targeting the reward and hunger pathways in the brain.

Dosing and titration: The medication is titrated gradually over four weeks to improve tolerability, reaching the target maintenance dose of 2 tablets twice daily (each tablet containing naltrexone 8 mg / bupropion 90 mg) by week 4, as follows per the SmPC:

• Week 1: 1 tablet each morning

• Week 2: 1 tablet morning, 1 tablet evening

• Week 3: 2 tablets morning, 1 tablet evening

• Week 4 onwards: 2 tablets morning, 2 tablets evening

Administration guidance: Tablets must be swallowed whole — do not crush, chew, or divide them. Mysimba should not be taken with a high-fat meal, as this significantly increases drug exposure and may raise the risk of adverse effects including seizures.

Mysimba is a prescription-only medicine and should only be used under the supervision of a qualified healthcare professional as part of a comprehensive weight management programme that includes dietary and physical activity support. It is not a standalone treatment. Patients should report any suspected adverse reactions via the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk or via the Yellow Card app.

Using Mysimba After Bariatric Surgery: Key Considerations

Mysimba use after bariatric surgery requires specialist MDT assessment, as altered gastrointestinal anatomy affects drug absorption and there is limited clinical trial data in post-bariatric populations.

The use of Mysimba following bariatric surgery is a clinically complex area that requires careful, individualised assessment by a specialist multidisciplinary team (MDT). Bariatric procedures — including Roux-en-Y gastric bypass (RYGB), sleeve gastrectomy, and adjustable gastric banding — significantly alter gastrointestinal anatomy and physiology, which can affect how medications are absorbed, distributed, and metabolised.

Some patients who have undergone bariatric surgery experience weight regain over time, which may prompt consideration of adjunctive pharmacological therapies. Where a patient continues to meet the licensed BMI criteria with relevant comorbidities, use of Mysimba may fall within the licensed indication rather than constituting off-label prescribing. However, there is currently limited clinical trial data specifically evaluating the safety and efficacy of naltrexone/bupropion in post-bariatric patients, and neither NICE nor the MHRA has issued specific guidance addressing this combination in this population. Specialist oversight and shared decision-making are therefore essential.

Pharmacotherapy is generally considered once weight has stabilised or significant regain is established, nutritional deficiencies have been identified and addressed, and the patient is engaged with a structured lifestyle programme — typically within a specialist bariatric MDT.

Key clinical considerations include:

• Type of surgery performed: Malabsorptive procedures such as RYGB are more likely to affect drug absorption than purely restrictive procedures.

• Time since surgery: The post-operative period involves significant physiological adaptation; pharmacotherapy is not initiated in the immediate post-surgical phase.

• Concurrent medications: Post-bariatric patients often take nutritional supplements and other medications; potential interactions must be reviewed carefully (see below).

• Patient suitability and contraindications: The following are contraindications or important cautions per the Mysimba SmPC and must be thoroughly assessed before prescribing:

• Current or recent (within 14 days) use of monoamine oxidase inhibitors (MAOIs)
• Seizure disorder or conditions that lower seizure threshold
• Uncontrolled hypertension
• Eating disorders (current or history of anorexia nervosa or bulimia nervosa)
• Bipolar disorder or history of mania
• Severe hepatic impairment
• End-stage renal disease
• Opioid dependence or acute opioid withdrawal
• Pregnancy or breastfeeding (see safety section)
• Abrupt withdrawal from alcohol or benzodiazepines
• Concomitant use of other bupropion-containing products

Any decision to initiate Mysimba after bariatric surgery should be made collaboratively between the patient and a specialist with expertise in both obesity medicine and post-bariatric care, with reference to BOMSS (British Obesity and Metabolic Surgery Society) guidance and the Specialist Pharmacy Service (SPS) recommendations on prescribing after bariatric surgery.

Absorption and Pharmacokinetic Changes Following Bariatric Procedures

Roux-en-Y gastric bypass significantly disrupts absorption of modified-release tablets like Mysimba, potentially causing unpredictable plasma drug levels; UK SPS and BOMSS guidance advises avoiding such formulations after malabsorptive procedures where possible.

Bariatric surgery fundamentally alters the gastrointestinal tract, and these anatomical changes can have profound effects on drug pharmacokinetics — the processes of absorption, distribution, metabolism, and excretion. Understanding these changes is essential when considering any oral medication in post-bariatric patients.

Roux-en-Y gastric bypass is particularly significant from a pharmacokinetic standpoint. It reduces gastric volume, bypasses the duodenum and proximal jejunum (key sites of drug absorption), alters gastric pH, and accelerates gastric emptying. These changes can lead to either reduced or increased drug bioavailability depending on the medication's physicochemical properties.

Mysimba is formulated as a prolonged-release (modified-release) tablet, which presents a specific concern in post-bariatric patients. Modified-release formulations rely on intact gastrointestinal transit and surface area for controlled drug delivery. Following procedures that shorten intestinal transit time or reduce absorptive surface area, the release mechanism may be disrupted, potentially resulting in:

• Unpredictable plasma drug concentrations — either subtherapeutic levels reducing efficacy, or elevated peaks increasing adverse effect risk.

• Altered peak concentration timing, which may affect both tolerability and clinical response.

UK professional guidance from the Specialist Pharmacy Service (SPS) and BOMSS advises that modified-release and enteric-coated formulations should be avoided where possible after malabsorptive procedures such as RYGB, as their absorption can be unreliable. Clinicians should weigh this carefully when considering Mysimba in this context.

Where absorption concerns are significant, it may be appropriate to consider alternative anti-obesity pharmacotherapies that are less dependent on gastrointestinal absorption — for example, GLP-1 receptor agonists administered by subcutaneous injection (such as semaglutide or liraglutide, where locally commissioned). This should be discussed within the specialist MDT.

Sleeve gastrectomy, while less disruptive to absorption than RYGB, still reduces gastric volume and may alter gastric emptying rates. Adjustable gastric banding has comparatively fewer pharmacokinetic implications but is now less commonly performed in the UK.

Given these complexities, close clinical monitoring of both efficacy (weight response) and safety (blood pressure, heart rate, and adverse effects) is advisable if Mysimba is prescribed post-bariatric surgery. There is no validated therapeutic drug monitoring protocol for naltrexone/bupropion, and routine plasma level measurement is not recommended. Crushing or splitting prolonged-release tablets is not recommended and may alter the drug's release profile unpredictably, as well as increasing seizure risk.

Risks, Side Effects, and Safety Monitoring Post-Surgery

Key risks include seizures, elevated blood pressure, opioid receptor blockade, CYP2D6 drug interactions, and worsening nutritional deficiencies; blood pressure, liver function, nutritional status, and mood should be monitored regularly.

Mysimba carries a range of potential adverse effects that are relevant in any patient population, but these warrant heightened attention in individuals who have undergone bariatric surgery due to their altered physiology and often complex medical backgrounds.

Common side effects of naltrexone/bupropion include:

• Nausea and vomiting (particularly during dose titration)

• Headache and dizziness

• Constipation or diarrhoea

• Insomnia and dry mouth

• Increased blood pressure and heart rate

Nausea is especially pertinent in post-bariatric patients, who may already be prone to gastrointestinal symptoms. Persistent vomiting can exacerbate nutritional deficiencies — a recognised risk following bariatric surgery — and may compromise the absorption of essential vitamins and minerals such as vitamin B12, iron, calcium, and folate.

Seizure risk: Bupropion lowers the seizure threshold. This is a significant safety concern in post-bariatric patients who may have experienced rapid weight loss, electrolyte imbalances, or who are taking other medications that also lower seizure threshold. Mysimba must not be taken with a high-fat meal, as this increases bupropion exposure and further raises seizure risk. A personal or family history of seizures is a contraindication.

Opioid interactions: Naltrexone blocks opioid receptors and will precipitate acute withdrawal in patients dependent on opioids. It also renders opioid-based analgesia ineffective, which has important implications for post-surgical pain management. Patients taking Mysimba should carry information (e.g., a medicines alert card) indicating that they are taking an opioid antagonist, so that healthcare professionals are aware in emergency situations.

Drug interactions — CYP2D6 inhibition: Bupropion is a potent inhibitor of the CYP2D6 enzyme. This can significantly increase plasma concentrations of co-administered medicines metabolised by this pathway, including certain antidepressants (e.g., tricyclic antidepressants, some SSRIs), antipsychotics, metoprolol, and tamoxifen. A full medicines review is essential before initiation. Concomitant use of other bupropion-containing products must be avoided.

MAOI restriction: Mysimba must not be started within 14 days of stopping an MAOI, due to risk of serious hypertensive reactions.

Hepatic effects: Naltrexone undergoes hepatic metabolism and has been associated with hepatotoxicity at higher doses. Liver function should be assessed where clinically indicated. Patients should be advised to seek prompt medical attention if they develop symptoms suggestive of hepatitis, such as jaundice, dark urine, or right upper quadrant pain.

Pregnancy and breastfeeding: Mysimba is contraindicated in pregnancy and breastfeeding. Women of childbearing potential should use effective contraception during treatment. If pregnancy occurs or is planned, treatment should be stopped immediately and medical advice sought without delay.

Neuropsychiatric effects: Bupropion carries a warning regarding mood changes, including low mood, anxiety, agitation, and suicidal ideation. Patients and carers should be advised to monitor for these changes and seek prompt medical review if they occur.

Safety monitoring recommendations:

• Blood pressure and heart rate checks before initiation and at regular intervals during treatment

• Liver function tests where clinically indicated

• Regular review of nutritional status and supplementation adequacy

• Monitoring for mood changes, low mood, or suicidal ideation

• Full medicines reconciliation including CYP2D6 interaction check at initiation and when any new medicine is added

Stopping rule: Patients should be reviewed at 16 weeks. If clinically meaningful weight loss of at least 5% of initial body weight has not been achieved, Mysimba should be discontinued, as continued treatment is unlikely to be beneficial.

Suspected adverse reactions should be reported via the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk or via the Yellow Card app.

NICE and NHS Guidance on Weight Management After Bariatric Surgery

There is no NICE technology appraisal recommending routine NHS commissioning of Mysimba; NICE has appraised semaglutide (TA875) and liraglutide (TA664) as alternatives, and NHS availability of Mysimba varies by integrated care board.

In the United Kingdom, weight management following bariatric surgery is guided primarily by NICE guideline CG189 (Obesity: identification, assessment and management), which recommends that patients who have undergone bariatric surgery receive long-term follow-up as part of a structured care programme. This includes dietary support, psychological input, physical activity guidance, and monitoring for nutritional deficiencies. Weight regain is acknowledged as a recognised long-term challenge.

Regarding pharmacotherapy, it is important to note that there is currently no NICE technology appraisal recommending routine NHS commissioning of naltrexone/bupropion (Mysimba). NICE has, however, appraised other pharmacological options for weight management:

• NICE TA875 recommends semaglutide 2.4 mg (Wegovy) as an option for weight management in adults meeting specified criteria, subject to specialist MDT oversight.

• NICE TA664 recommends liraglutide 3 mg (Saxenda) as an option in adults meeting specified criteria.

Clinicians considering Mysimba for post-bariatric patients should refer to the EMA Summary of Product Characteristics (SmPC) for full prescribing information. Where a patient continues to meet the licensed BMI and comorbidity criteria, use of Mysimba may fall within the licensed indication; however, given the limited evidence base in post-bariatric populations, specialist oversight and shared decision-making are essential rather than routine prescribing.

The MHRA has not issued specific safety communications regarding Mysimba use after bariatric surgery, and there is no specific contraindication listed for post-bariatric patients as a class. Nevertheless, the absence of a specific contraindication does not imply established safety in this population, and prescribing should always involve specialist review.

NHS commissioning of Mysimba varies by integrated care board (ICB); patients should check local formulary availability with their GP or specialist team. Long-term post-bariatric follow-up should be delivered through a specialist bariatric MDT in line with BOMSS (British Obesity and Metabolic Surgery Society) guidance and NHS post-bariatric care pathways.

When to Speak to Your Specialist or GP

Patients should contact their GP or bariatric specialist promptly if they experience seizures, severe nausea, mood changes, signs of nutritional deficiency, or symptoms of liver problems, and must seek urgent care for chest pain or sudden severe headache.

If you have had bariatric surgery and are considering or currently taking Mysimba (naltrexone/bupropion), it is important to maintain open communication with your healthcare team. This medication should never be started, adjusted, or discontinued without professional guidance, particularly given the pharmacokinetic complexities and safety considerations outlined above.

Contact your GP or bariatric specialist promptly if you experience:

• Persistent or severe nausea, vomiting, or abdominal pain

• New or worsening headache, particularly if accompanied by visual changes or a rise in blood pressure

• Seizures or unexplained episodes of loss of consciousness

• Significant mood changes, low mood, anxiety, agitation, or any thoughts of self-harm or suicide

• Signs of opioid withdrawal if you have recently used opioid-containing medications

• Symptoms suggestive of nutritional deficiency, such as fatigue, hair loss, tingling in the extremities, or poor wound healing

• Symptoms that may suggest a liver problem, such as yellowing of the skin or eyes (jaundice), dark urine, or pain in the upper right abdomen

Seek urgent medical attention if you experience chest pain, palpitations, or a sudden severe headache. Always inform emergency healthcare staff that you are taking naltrexone, as this affects the use of opioid-based pain relief.

If you are pregnant, planning a pregnancy, or become pregnant while taking Mysimba, stop the medication and contact your GP or specialist without delay. Mysimba is contraindicated in pregnancy and breastfeeding.

Your bariatric MDT — which may include a bariatric surgeon, specialist dietitian, clinical psychologist, and obesity physician — is best placed to review whether Mysimba is appropriate for your individual circumstances. They can assess your current nutritional status, review your full medication list for interactions, and determine whether the potential benefits outweigh the risks given your specific surgical history.

Regular follow-up appointments are essential. Do not assume that a medication that was well tolerated before surgery will behave in the same way afterwards. Proactive communication with your healthcare team is the cornerstone of safe and effective weight management following bariatric surgery.

If you experience a suspected side effect from Mysimba, you can report it directly to the MHRA via the Yellow Card Scheme at yellowcard.mhra.gov.uk or using the Yellow Card app.

Frequently Asked Questions