Naltrexone for Weight Loss + How Contrave Actually Works: Evidence Review

Naltrexone alone is not FDA-approved for weight loss — it is an opioid receptor antagonist approved for opioid use disorder and alcohol use disorder. Contrave, the fixed-dose combination of naltrexone HCl 8 mg + bupropion HCl 90 mg ER (two tablets twice daily at maintenance), is FDA-approved for chronic weight management since September 2014. In the pivotal COR-I phase 3 trial (Greenway et al., Lancet 2010, PMID 20673995), Contrave produced a mean body-weight loss of −6.1% at 56 weeks vs. −1.3% for placebo. That positions Contrave below the GLP-1 receptor agonists (Wegovy −14.9%, Zepbound −20.9%) but above orlistat (−3–5%), and it is a meaningful option for patients who cannot or will not use injectable GLP-1 medications. Below: the mechanism, the verbatim FDA label, the COR-I data, the full side-effect and warning profile, and how Contrave fits in 2026’s weight-loss landscape.

TL;DR — naltrexone alone vs. Contrave

Cross-trial caveat: the figures above are from independent trials with different populations, designs, and durations. They are not head-to-head comparisons and cannot be used to predict individual outcomes.

What is naltrexone?

Naltrexone is a pure opioid receptor antagonist — it competitively blocks mu, kappa, and delta opioid receptors in both the central nervous system and peripheral tissues. It has no agonist activity; it does not produce euphoria or physical dependence.

Naltrexone’s two FDA-approved indications are opioid use disorder (blocking the euphoric and analgesic effects of exogenously administered opioids) and alcohol use disorder (reducing the rewarding effects of alcohol via the opioid system). The standard dose for those indications is 50 mg/day orally, or 380 mg once monthly as Vivitrol (extended-release injectable naltrexone).

How does naltrexone relate to appetite? In the hypothalamus, pro-opiomelanocortin (POMC) neurons regulate appetite suppression. When POMC neurons fire, they release α-MSH (which suppresses appetite) and β-endorphin (an endogenous opioid). That β-endorphin feeds back onto the POMC neurons via autoreceptors, damping further POMC firing — a self-limiting negative feedback loop. Naltrexone blocks those opioid autoreceptors, removing the brake on POMC activity. In theory, POMC neurons fire more, releasing more appetite-suppressing α-MSH. In practice, the effect of naltrexone monotherapy on body weight is modest and the FDA has not approved it for this use.

Naltrexone is not a GLP-1 receptor agonist. It does not mimic the gut hormone GLP-1, does not slow gastric emptying, and does not activate the incretin pathway. The mechanism is entirely distinct from Wegovy, Zepbound, Saxenda, and Foundayo.

Naltrexone monotherapy evidence for weight loss

Naltrexone alone has been studied in small trials for weight loss with mixed and modest results. It is not FDA-approved for chronic weight management and should not be used as monotherapy for this purpose outside a physician-supervised off-label context.

The observed weight loss in monotherapy studies is generally in the range of ~3–5% at 16–28 weeks, with high variability across studies and significant overlap with placebo response. Limitations of the monotherapy evidence base include:

• Small sample sizes — most studies enrolled fewer than 100 participants, underpowered to detect modest effects reliably.
• Short duration — weight loss trials of 16–24 weeks cannot assess durability of effect or regain patterns.
• No dose standardization — monotherapy studies used doses ranging from 25 mg to 100 mg/day, complicating cross-study comparison.
• No FDA-approved indication — the prescribing information for naltrexone tablets lists opioid and alcohol use disorder as the only approved indications. Weight management is not listed.

The mechanistic rationale for why Contrave (the naltrexone + bupropion combination) substantially outperforms naltrexone monotherapy is covered in the mechanism section below. If your prescriber recommends naltrexone monotherapy for weight loss, it is reasonable to ask why the FDA-approved combination Contrave is not preferred — the published evidence base is substantially stronger.

What is Contrave (naltrexone + bupropion)?

Contrave is a fixed-dose extended-release tablet combining two FDA-approved active pharmaceutical ingredients:

• Naltrexone HCl 8 mg per tablet (opioid receptor antagonist)
• Bupropion HCl 90 mg ER per tablet (aminoketone antidepressant and dopamine/norepinephrine reuptake inhibitor)

At the maintenance dose of two tablets twice daily (four tablets total per day), the daily doses are 32 mg naltrexone + 360 mg bupropion.

Per the Contrave DailyMed label (SetID 485ff360-32c8-11df-928b-0002a5d5c51b), Section 1 Indications and Usage:

“CONTRAVE is indicated in combination with a reduced-calorie diet and increased physical activity to reduce excess body weight and maintain weight reduction long term in adults with:
• an initial body mass index (BMI) of 30 kg/m² or greater (obese), or
• an initial body mass index of 27 kg/m² or greater (overweight) in the presence of at least one weight-related comorbid condition (e.g., hypertension, type 2 diabetes mellitus, or dyslipidemia).
Limitations of Use: The effect of CONTRAVE on cardiovascular morbidity and mortality has not been established. The safety and effectiveness of CONTRAVE in combination with other products intended for weight loss, including prescription drugs, over-the-counter drugs, and herbal preparations, have not been established.”

Contrave (NDA 200063) received FDA approval on September 10, 2014. The original sponsor was Orexigen Therapeutics; the drug is now marketed by Currax Pharmaceuticals LLC (contact line: 1-800-793-2145). The DailyMed label identifies the current labeler as Nalpropion Pharmaceuticals LLC.

Bupropion, the second component, is best known as the antidepressant Wellbutrin (approved 1985) and smoking cessation aid Zyban. In Contrave, it functions in a synergistic mechanism with naltrexone to increase hypothalamic appetite suppression, described in detail below. Bupropion alone also causes modest weight loss relative to placebo, but the naltrexone + bupropion combination produces substantially greater effect than either drug alone.

How Contrave actually works (mechanism)

Per the Contrave DailyMed label, Section 12.1 Mechanism of Action:

“Combined, bupropion and naltrexone increased the firing rate of hypothalamic pro-opiomelanocortin (POMC) neurons in vitro, which are associated with regulation of appetite.”

“Naltrexone and bupropion have effects on two separate areas of the brain involved in the regulation of food intake: the hypothalamus (appetite regulatory center) and the mesolimbic dopamine circuit (reward system).”

“The exact neurochemical effects of naltrexone/bupropion leading to weight loss are not fully understood.”

The proposed synergy mechanism works as follows:

• Bupropion activates POMC neurons in the hypothalamic arcuate nucleus via dopaminergic and noradrenergic signaling. POMC neurons release α-MSH, which binds MC4R receptors and suppresses appetite. POMC neurons also release β-endorphin.
• Beta-endorphin autoreceptor brake: The β-endorphin released by POMC neurons feeds back onto opioid autoreceptors on the same POMC neurons, attenuating their own firing — a negative feedback loop that limits bupropion’s appetite-suppression effect when bupropion is used alone.
• Naltrexone removes the brake: By blocking the opioid autoreceptors, naltrexone prevents β-endorphin from suppressing POMC neuron activity. This allows bupropion’s stimulatory effect on POMC neurons to persist longer and at greater magnitude.
• Mesolimbic reward pathway: Bupropion also inhibits dopamine and norepinephrine reuptake in the reward circuit, potentially reducing the rewarding salience of food. Naltrexone contributes here as well by blocking opioid-mediated reward signals from palatable food.

This two-component synergy explains the COR-I trial finding that the naltrexone 32 mg + bupropion 360 mg combination (−6.1%) produced significantly greater weight loss than either component alone. The combination is mechanistically distinct from GLP-1 receptor agonists, which work primarily by activating the GLP-1 receptor in the brainstem and hypothalamus, slowing gastric emptying, and suppressing appetite through the incretin hormone pathway.

Contrave clinical evidence — COR-I trial

The pivotal efficacy trial is COR-I (Contrave Obesity Research I): Greenway FL et al., “Effect of naltrexone plus bupropion on weight loss in overweight and obese adults (COR-I): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial,” Lancet 2010; 376(9741):595–605. PMID: 20673995.

The COR-I result was consistent with the broader COR program. The Contrave DailyMed label (Section 6.1) notes that Contrave was evaluated for safety in five double-blind, placebo-controlled trials enrolling 4,754 overweight or obese patients (3,239 on Contrave, 1,515 on placebo) for a treatment period up to 56 weeks. The pattern across all trials: Contrave 32 mg/360 mg produced approximately 5–9% mean body-weight reduction depending on the trial (COR-I, COR-II, COR-BMOD, COR-Diabetes), versus 1–3% for placebo. The Contrave label requires discontinuation if a patient has not lost at least 5% of baseline body weight after 12 weeks at the maintenance dose.

Note on PMID: This article uses the verified PMID 20673995 for the COR-I Lancet publication. A widely circulated PMID “23633007” found in third-party summaries is incorrect — it points to an unrelated BMJ news article about a German transplant organization. We confirmed 20673995 by direct PubMed record lookup before publication.

Contrave dose ladder (verbatim from FDA label §2)

Contrave is titrated over four weeks to minimize nausea and other early side effects. Per the Contrave DailyMed label, Section 2 Dosage and Administration:

NTX = naltrexone HCl; BUP = bupropion HCl ER. Per the label, Contrave tablets should be swallowed whole and not cut, chewed, or crushed. High-fat meals increase bupropion systemic exposure significantly (the label warns of a potential increased seizure risk) and Contrave should not be taken with a high-fat meal. If patients miss a dose, they should skip the missed dose and take the next dose at the scheduled time; do not take two doses at once.

Contrave side effects and boxed warning

Boxed warning: suicidal thoughts and behaviors

Contrave carries an FDA black box warning because of its bupropion component. Bupropion is an antidepressant (the active ingredient in Wellbutrin and Zyban), and antidepressants as a class carry a mandated boxed warning. Per the Contrave DailyMed label boxed warning:

WARNING: SUICIDAL THOUGHTS AND BEHAVIORS“Antidepressants increased the risk of suicidal thoughts and behavior in children, adolescents, and young adults in short-term trials. Monitor closely for worsening, and for the emergence of suicidal thoughts and behaviors. CONTRAVE is not approved for use in pediatric patients.”

Importantly, the COR-I trial reported that “combination treatment was not associated with increased depression or suicidality events compared with placebo” (Greenway et al., PMID 20673995). The boxed warning reflects the class label requirement for all bupropion-containing products, not a signal specifically observed in the Contrave weight-loss trials. Nonetheless, clinicians are required to monitor patients — particularly younger adults — for worsening mood or emergence of suicidal ideation when initiating or adjusting Contrave.

Most common adverse reactions (≥5% incidence)

Per the Contrave DailyMed label, Section 6.1 Adverse Reactions (occurring in ≥5% of Contrave-treated patients and at twice the placebo rate):

Nausea (32.5%) is by far the most common adverse event and is the primary driver of early discontinuation. The 4-week titration schedule is specifically designed to reduce the likelihood of severe nausea; most patients who experience nausea during titration report improvement once at the maintenance dose. Taking Contrave with food (but not high-fat food) can reduce nausea.

Seizure risk

Per the Contrave label Section 5.3: “Bupropion, a component of CONTRAVE, can cause seizures. The risk of seizure is dose-related.” The seizure incidence in clinical trials was approximately 0.1% with Contrave vs. 0% placebo. Risk is increased by: prior seizure history, eating disorders (anorexia nervosa, bulimia), abrupt discontinuation of alcohol or benzodiazepines, and use of medications that lower the seizure threshold. Patients with a seizure disorder should not take Contrave.

Blood pressure and heart rate

Per the Contrave label Section 5.5: “CONTRAVE can cause an increase in systolic and/or diastolic blood pressure as well as an increase in resting heart rate.” Blood pressure and pulse should be measured before starting Contrave and monitored during treatment. Contrave is contraindicated in uncontrolled hypertension.

Contraindications (Section 4, verbatim)

Per the Contrave DailyMed label, Section 4, Contrave is contraindicated in patients with:

• Uncontrolled hypertension
• Seizure disorders, or a history of seizures
• Anorexia nervosa or bulimia nervosa (current or history) — bupropion risk of seizure is higher in eating disorder patients
• Abrupt discontinuation of alcohol, benzodiazepines, barbiturates, or antiepileptic drugs (seizure risk during withdrawal)
• Use of other bupropion-containing products (e.g., Wellbutrin, Zyban, Aplenzin) — risk of dose-dependent adverse effects including seizure
• Chronic opioid use or use of partial opioid agonists (e.g., methadone, buprenorphine) — the naltrexone component can precipitate acute opioid withdrawal
• Monoamine oxidase inhibitor (MAOI) use within the preceding 14 days — risk of hypertensive crisis
• Known hypersensitivity to naltrexone, bupropion, or any component of the formulation
• Severe hepatic impairment

The opioid-use contraindication is clinically important: patients who are currently on opioid pain medication, methadone maintenance, or buprenorphine/naloxone (Suboxone) for opioid use disorder cannot take Contrave. The naltrexone component will precipitate acute withdrawal. A minimum opioid-free interval of 7 to 10 days for short-acting opioids (and longer for long-acting opioids) is required before initiating Contrave. This is also why naltrexone monotherapy cannot be used in opioid-dependent patients without completing detoxification first.

How Contrave compares to GLP-1 shots

Cross-trial caveat (mandatory read): The efficacy numbers below come from independent, separately conducted trials with different patient populations, enrollment criteria, background therapy requirements, and follow-up durations. These are not head-to-head trial results. They provide a general order-of-magnitude framework, not a precise comparison. No published randomized head-to-head trial between Contrave and any GLP-1 agonist exists as of May 2026.

On raw efficacy, Contrave sits below all the GLP-1 injections. However, raw efficacy is not the only clinical decision variable. Contrave has meaningful advantages in specific patient contexts:

• No injection required. Patients with needle phobia or injection-site concerns can use Contrave without any subcutaneous injection.
• Lower monthly cost. Contrave’s manufacturer savings programs can bring the out-of-pocket cost below $100–$200/month — substantially less than brand-name GLP-1 injectables before manufacturer programs are applied.
• No GLP-1 contraindications. Patients with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia type 2 (MEN2) are contraindicated from GLP-1 receptor agonists. Contrave carries no such warning.
• No pancreatitis contraindication. Patients with a history of pancreatitis are generally counseled against GLP-1 RAs; Contrave does not share this concern.
• Dual-purpose psychiatric benefit potential. For patients who also have depression or nicotine dependence, bupropion is an FDA-approved treatment for both — a prescriber may discuss Contrave’s dual mechanism as a clinical consideration.

For a comprehensive non-GLP-1 vs. GLP-1 comparison including Qsymia, orlistat, and phentermine, see our Best FDA-approved appetite suppressant 2026 evidence review. For GLP-1 alternatives specifically for patients displaced from Wegovy or Zepbound, see our Wegovy alternatives evidence guide.

Who Contrave is and is not right for

Patients who may benefit most from Contrave

• Patients who cannot tolerate or self-administer GLP-1 injections (needle phobia, injection-site reactions, logistics barriers)
• Patients contraindicated from GLP-1 RAs (MTC/MEN2 history, prior pancreatitis, severe GI motility disorder)
• Patients who are already taking bupropion for depression or smoking cessation and want weight management added (discuss with prescriber: cannot duplicate bupropion)
• Patients who experience significant food cravingsand reward-driven eating (the mesolimbic dopamine component of Contrave’s mechanism targets this)
• Patients who need a lower-cost FDA-approved optionwhile waiting for insurance coverage of GLP-1s

Patients who should NOT take Contrave

• Patients with a seizure disorder or seizure history(bupropion is contraindicated)
• Patients with active anorexia nervosa or bulimia nervosa (both are absolute contraindications per the label)
• Patients currently taking opioid pain medication, methadone, or buprenorphine/naloxone (naltrexone will precipitate withdrawal)
• Patients taking MAOIs or who have taken them within 14 days
• Patients already taking another bupropion-containing product (Wellbutrin, Zyban, Aplenzin)
• Patients with uncontrolled hypertension
• Patients with severe hepatic impairment
• Patients who are pregnant — both bupropion and naltrexone are classified in prior FDA pregnancy categories suggesting potential fetal risk
• Patients under 18 — Contrave is not approved for pediatric use (unlike Qsymia, which has a 12+ indication)

Contrave cost and insurance coverage

Contrave’s insurance coverage situation is more favorable than GLP-1 injectables in several respects: it is a lower-cost drug, has been available longer (since 2014), and does not face the same level of formulary resistance that Wegovy and Zepbound do. However, coverage varies significantly by plan.

Cash-pay and savings programs

• Currax patient savings card: Available through Currax Pharmaceuticals (1-800-793-2145). Eligible commercially insured patients can reduce out-of-pocket costs. Cash-pay patients using manufacturer savings programs have reported approximately $100–$200/month depending on pharmacy and program tier. Verify directly with Currax, as program terms change.
• GoodRx and retail coupons: Generic naltrexone + bupropion is not available as a combined product — Contrave’s formulation is proprietary ER. GoodRx pricing for brand Contrave varies widely by zip code; check current pricing at your specific pharmacy.
• Medicare Part D: Contrave, like all FDA-approved weight-loss drugs, is excluded from Medicare Part D coverage under the statutory exclusion for “weight loss” medications in 42 U.S.C. § 1395w-102(e)(2)(A), unless the drug is being used for a non-weight-loss FDA-approved indication (e.g., bupropion alone for depression via a separate prescription). As of May 2026, the CMMI MISUSE model and CMS demonstration projects under discussion do not yet extend coverage to Contrave.

For a comprehensive walkthrough of insurance dynamics for weight-loss medications, see our GLP-1 insurance coverage: Medicare, Medicaid, and commercial guide.

Naltrexone alone for weight loss — when (if ever) is it appropriate?

Prescribing naltrexone monotherapy for weight loss is entirely off-label. The FDA has not approved naltrexone — at any dose or formulation — for chronic weight management. There is no NDA, no FDA-reviewed clinical data package, and no mandated dosing protocol for this use.

Small investigational studies have reported 3–5% weight loss with naltrexone 50 mg/day over 16–28 weeks, but these studies have methodological limitations (small N, heterogeneous populations, short duration) and do not constitute the evidence standard that supports prescribing for chronic weight management.

The practical question for any patient whose prescriber recommends naltrexone monotherapy for weight loss is: why not Contrave? Contrave contains naltrexone plus bupropion, has a substantially larger evidence base (four phase 3 trials, 4,754 patients), carries an FDA approval for chronic weight management, and has a manufacturer savings program. A prescriber recommending naltrexone monotherapy for weight loss may have a specific clinical rationale (e.g., patient currently on bupropion for depression, cannot add a second bupropion-containing product), but that rationale should be explicit.

Low-dose naltrexone (LDN, 1.5–4.5 mg/day) is a separate off-label practice that has generated interest for inflammatory, autoimmune, and neurological conditions. Evidence for LDN specifically for weight loss is limited to preclinical and anecdotal reports; there is no substantive clinical trial evidence for this use as of 2026. LDN is distinct from the 50 mg/day dose used in the monotherapy weight-loss studies and from the 32 mg/day naltrexone dose in Contrave.

Frequently asked questions

Related research

• Best FDA-approved appetite suppressant 2026: evidence-ranked comparison — Zepbound through phentermine, evidence-ranked with verbatim trial data.
• Qsymia (phentermine + topiramate ER) evidence review — the strongest non-GLP-1 oral option; CONQUER/EQUIP/SEQUEL trial data verbatim.
• Wegovy alternatives guide: non-GLP-1 FDA-approved options — for patients displaced from Wegovy who need an alternative.
• Tirzepatide vs. semaglutide head-to-head evidence review — for patients comparing the two leading GLP-1 options.
• GLP-1 insurance coverage: Medicare, Medicaid, and commercial guide — full insurance landscape for all FDA-approved weight-loss medications.
• GLP-1 injection beginner guide — if you are deciding between Contrave (oral) and a GLP-1 injection, this guide explains what GLP-1 shots involve.
• Wellbutrin XL for weight loss: how fast and how much? (evidence review) — the companion article for bupropion monotherapy. Wellbutrin XL shares bupropion with Contrave but is not FDA-approved for weight loss; typical effect in MDD trials is ~3–5 lb vs. Contrave’s −6.1% in COR-I.

Important disclaimer. This article is educational and does not constitute medical advice. Every clinical claim is sourced from the verbatim Contrave FDA label (DailyMed SetID 485ff360-32c8-11df-928b-0002a5d5c51b) or published peer-reviewed phase 3 trial data with directly verified PMIDs. The choice of whether to start, adjust, or stop any weight-loss medication — including Contrave or any naltrexone-containing product — must be made with a licensed prescriber who has reviewed your full medical history, current medications, and contraindications. Efficacy figures reflect published population means; individual response will vary. Drug pricing and manufacturer program terms are current as of May 2026 and subject to change. Weight Loss Rankings does not provide medical advice, diagnosis, or treatment.