2026-08-25 · contrave, qsymia, phentermine, anti-obesity medication, naltrexone-bupropion, phentermine-topiramate, sympathomimetic, obesity medicine

Which is the most effective for weight loss: Contrave, Qsymia, or Phentermine?

Qsymia is the strongest of the three on trial-controlled data. In CONQUER (Gadde 2011, The Lancet, n=2,487, 56 weeks), top-dose Qsymia 15/92 mg produced roughly 9–11% placebo-adjusted weight loss. Contrave 32/360 mg produced about 5% placebo-adjusted loss in COR-I (Greenway 2010, The Lancet, n=1,742, 56 weeks). Phentermine monotherapy produces roughly 5–10% weight loss at 12 weeks in most trials (dose- and duration-dependent), but has no controlled 56-week comparator because its FDA label is short-term only. Ranking at maximum tolerated dose over 12 months: Qsymia > Contrave ≈ Phentermine. None reaches semaglutide 2.4 mg (~15%) or tirzepatide 15 mg (~21%).

Which is the cheapest of the three in 2026?

Phentermine is by far the cheapest. Generic phentermine hydrochloride 37.5 mg runs $15–$40 per month cash pay through pharmacy discount programs — no coupons or manufacturer program needed. Contrave brand runs about $99/month through the Currax direct-pay bundled coupon, or roughly $25/month with commercial insurance and prior authorization. Qsymia brand runs $200–$285/month through the Vivus Qsymia Advantage direct-pay program; commercial-insurance copay assist caps at $70. All three fail Medicare Part D's obesity-drug exclusion, so seniors typically pay full cash unless they have secondary coverage that carves out obesity medications.

Which is safest?

Safety depends heavily on the patient. Contrave carries a boxed warning for suicidal thoughts and behaviour (inherited from bupropion) and is contraindicated in patients on chronic opioids. Qsymia carries a REMS teratogenicity program (topiramate causes a 2- to 3-fold increased risk of first-trimester cleft palate) and is contraindicated in pregnancy. Phentermine has no boxed warning but is pregnancy category X, DEA Schedule IV, and contraindicated in coronary artery disease, uncontrolled hypertension, arrhythmias, and heart failure. There is no single-safest choice — each has a decision-driving contraindication that rules it out for a specific population. The right question is which safety profile is compatible with your history.

Can I take Phentermine long-term?

Legally in the US, yes — off-label. The FDA label for phentermine is short-term (up to 12 weeks) and dates to a 1959 approval that has never been updated. There is no pharmacological reason phentermine cannot be used longer: Hendricks 2011 (Obesity) followed 269 patients on continuous phentermine for up to 21 months and found no tachyphylaxis, no cardiovascular safety signal, and durable weight loss. The 2016 AACE Obesity Clinical Practice Guideline and the 2022 ASBP position statement both endorse long-term off-label use with monitoring. Many US prescribers use phentermine chronically or in a 12-weeks-on / 4-weeks-off cycle. Insurance coverage, DEA prescribing conventions, and some state pharmacy boards still enforce the 12-week label, so it remains a clinician-judgement call rather than a routine one.

Do any of these three work as well as Ozempic, Wegovy, Zepbound, or Mounjaro?

No. On trial-controlled 12-month weight loss, Qsymia (~10%) is the closest of the three, but semaglutide 2.4 mg (Wegovy at ~15% in Wilding 2021 STEP-1, NEJM) and tirzepatide 15 mg (Zepbound at ~21% in Jastreboff 2022 SURMOUNT-1, NEJM) both exceed it. Contrave and phentermine come in lower still, at roughly 5–7%. The honest framing: the three non-GLP-1 orals are meaningfully less effective than modern GLP-1 injectables. Their case for use in 2026 is cost, coverage denial for GLP-1s, GLP-1 contraindications (personal or family history of medullary thyroid cancer, active pancreatitis history), severe GI intolerance to the GLP-1 class, or a specific mechanistic fit — not head-to-head efficacy.

Can I use one of these three if GLP-1s made me too nauseated?

Yes, and it is one of the most common reasons to reach for them. All three of Contrave, Qsymia, and Phentermine work through mechanisms unrelated to gastric emptying, so the delayed-gastric-emptying nausea that dominates GLP-1 tolerability does not carry over. Contrave still has meaningful nausea (~30% in COR trials) from bupropion, but the pattern is different from GLP-1 nausea. Qsymia and phentermine have low GI side-effect burdens; their tolerability issues sit elsewhere — cognitive dulling and paresthesia for Qsymia, insomnia and elevated heart rate for phentermine. See our guide on [managing GLP-1 side effects](/weight-loss/managing-glp-1-side-effects/) for GI-adjunct strategies if you want to try to stay on a GLP-1 before switching class.

Which is the best choice if I have depression?

Contrave, in most cases. The bupropion component of Contrave (naltrexone-bupropion) is itself an FDA-approved antidepressant for major depressive disorder, so Contrave can serve double duty for the depressed patient who also needs weight-loss support. Bupropion is one of the few antidepressants that is weight-neutral to modestly weight-lowering, unlike most SSRIs which can drive weight gain. Do note the boxed warning for suicidal thoughts in patients aged 24 and under, and screen mood carefully at baseline and follow-up. Phentermine can worsen anxiety and insomnia and is generally avoided in active anxiety or agitated depression. Qsymia has no direct antidepressant effect and can add cognitive dulling that some patients with depression find intolerable.

Which is the best choice if I have a history of migraine?

Qsymia, because topiramate — its second active ingredient — is an FDA-approved migraine prophylactic drug in its own right. For the patient with obesity plus chronic migraine, Qsymia can serve double duty and often lets a separate topiramate prescription be discontinued. Practical dose note: Qsymia's top dose 15/92 mg delivers 92 mg of extended-release topiramate daily, at the low end of the migraine-prophylaxis range (typically 100 mg/day). The mid-dose 11.25/69 mg is also in a therapeutic range for migraine. Contrave and phentermine offer no migraine-prophylactic benefit.

Contrave vs Qsymia vs Phentermine

The one-sentence answer

Qsymia (phentermine-topiramate) delivers the most weight loss of the three — roughly 9–11% placebo-adjusted at 56 weeks — Contrave (naltrexone-bupropion) sits in the middle at about 5–6%, and Phentermine alone is the cheapest and fastest to prescribe at roughly 5–10% over 12 weeks; the safety profile — not the efficacy — usually decides which one fits. All three are the practical fallbacks when a GLP-1 is not affordable, not covered, or not appropriate. For the fuller landscape of non-GLP-1 options, see prescription weight-loss medications.

How Contrave, Qsymia, and Phentermine compare at a glance

The three drugs share almost nothing mechanistically — a mixed opioid-antagonist plus atypical antidepressant, a sympathomimetic plus GABA-modulator, and a bare sympathomimetic. That is why they are useful as a set: the failure modes barely overlap, so if one is ruled out on safety, another usually is not.

Placebo-adjusted efficacy compared

The three drugs are best ranked at the maximum FDA-labeled dose over the longest trial durations available. Head-to-head randomized data across all three does not exist; the numbers below are drawn from each drug’s pivotal program.

Ranking: Qsymia > Contrave > Phentermine on trial-controlled efficacy at 56 weeks; phentermine is not approved for chronic use in the US, so 56-week data do not exist by design. The Qsymia edge over Contrave is roughly 4 percentage points at the same 56-week endpoint — meaningful in practice. Phentermine’s numbers look competitive at 12 weeks but should not be read as a chronic-use comparison. The comorbidity-subgroup extensions — Aronne 2013 EQUIP for Qsymia + BMI ≥ 35, Apovian 2013 COR-II for Contrave — broadly reproduce the pivotal numbers with modest condition-specific tails.

Mechanism differences that matter clinically

The mechanisms are genuinely different, and each one predicts which eating pattern a drug will work best on.

• Phentermine — a sympathomimetic amine that releases norepinephrine in the hypothalamus, which suppresses appetite via central satiety centers. Fast-acting (hours), fatigue-forward mechanism, and the reason phentermine “feels like something” to most patients within days rather than weeks.
• Qsymia — phentermine + extended-release topiramate. Topiramate adds three mechanisms on top of phentermine’s satiety effect: GABA-A modulation, glutamate blockade, and weak carbonic anhydrase inhibition. That three-way delta is why Qsymia produces roughly twice the weight loss of phentermine monotherapy at 12 weeks — the drugs are complementary, not additive of the same pathway.
• Contrave — naltrexone + bupropion. Naltrexone antagonizes the opioid receptors in the mesolimbic reward circuit. Bupropion inhibits dopamine and norepinephrine reuptake, adding a stimulant-like satiety effect. The combination targets reward-driven and emotional eating specifically — snacking on highly palatable foods, evening grazing, cravings that dominate over true hunger. This is the mechanistic case for Contrave over the other two: if the eating pattern is reward-forward rather than hunger-forward, Contrave has a mechanism the others don’t. For pattern-based context see emotional eating and weight loss and sugar cravings and weight loss.

Cost in 2026

Cost is the reason many patients end up on one of these three in the first place — a covered GLP-1 is close to $0 for many insured patients, and an uncovered GLP-1 is $500–$1,000/month. The three non-GLP-1 orals sit far below both.

Phentermine is the cheapest by an order of magnitude and does not require any coupon program. Contrave’s direct-pay bundle is the most patient-friendly of the two branded options. Qsymia is the most expensive of the three and typically requires either commercial insurance or willingness to pay ~$200/month direct. For a fuller multi-brand walkthrough, prescription weight-loss medications compares the whole class.

Safety and boxed warnings compared

Each of the three carries a distinct decision-driving safety concern. These are not scare-text — they are the specific rule-outs prescribers use every day.

• Contrave — boxed warning for suicidal thoughts and behaviour, inherited from bupropion. Highest risk in patients aged 24 and under. Requires baseline mood screen, a clear plan for new or worsening depression, and immediate discontinuation and clinician contact if symptoms appear. Contrave is also contraindicated with chronic opioids (analgesic block plus precipitated withdrawal), with seizure disorders, uncontrolled hypertension, active or prior eating disorder (bulimia, anorexia), and within 14 days of an MAOI.
• Qsymia — teratogenicity boxed warning + mandatory REMS enrollment. Topiramate causes a roughly 2- to 3-fold increased risk of first-trimester cleft lip/cleft palate (Chen 2009, AJOG; Hernandez-Diaz 2012, Neurology). The REMS program requires prescriber and pharmacy certification, teratogenicity counselling, effective contraception, and a baseline plus monthly pregnancy test in women of childbearing potential. Also contraindicated in glaucoma, hyperthyroidism, and within 14 days of an MAOI.
• Phentermine — no boxed warning, but pregnancy category X and DEA Schedule IV. Contraindicated in coronary artery disease, uncontrolled hypertension, arrhythmias, and heart failure. Baseline BP and HR and monthly monitoring while on therapy are standard. The Hendricks 2011 cohort of 269 patients on chronic phentermine (up to 21 months) found no significant BP or HR change and no cardiovascular events, but the population screened out CV disease at baseline — the contraindication holds.

There is no single safest choice. The right question is which of the three safety profiles is compatible with the patient in front of you.

The 12-week rule (Phentermine specific)

Phentermine’s FDA approval is short-term — up to 12 weeks. The rule dates to a 1959 approval that has never been updated for chronic use, in an era when short trial durations were the only data available.

The clinical reality in 2026 is different. Many US prescribers use phentermine off-label for chronic weight management, which is legal but off-label. The evidence supporting that practice comes from Hendricks 2011 in Obesity — a 269-patient open-label EHR cohort followed on continuous phentermine for up to 21 months with no tachyphylaxis, no cardiovascular safety signal, and durable weight loss — and from the 2016 AACE Obesity Clinical Practice Guideline and 2022 ASBP position statement, both of which endorse long-term off-label use with monitoring.

This is the single most confusing aspect of the non-GLP-1 oral class, and the most common source of patient-prescriber misalignment. Insurance coverage, DEA prescribing conventions, and some state pharmacy boards still enforce the 12-week label; some prescribers cycle patients 12-weeks-on / 4-weeks-off to formally comply with it; others prescribe chronically and document off-label rationale. See our full phentermine guide for the mechanics and monitoring.

Side effect profile compared

The side-effect families barely overlap — another reason the three drugs act as a mutual fallback set.

Practical readouts: Contrave’s tolerability is dominated by GI symptoms (nausea, constipation) and headache — nausea is the most common reason for early discontinuation and usually attenuates over 4 to 8 weeks. Taking Contrave with a low-fat meal helps; a high-fat meal raises bupropion exposure enough to increase seizure risk. Qsymia’s tolerability is dominated by paresthesia and cognitive dulling — the “topiramate footprint” that patients describe as tingling in the hands and feet plus mild word-finding difficulty; both are dose-dependent and often improve within weeks. Phentermine’s tolerability is dominated by dry mouth, insomnia, and mild-to-moderate anxiety — take in the morning, not the evening, and hydrate. For GI-focused framing that applies especially to Contrave, see managing GLP-1 side effects — the anti-nausea playbook there transfers with minor adjustments.

When Contrave is the better answer

Three concrete cases where Contrave usually wins:

1. Reward-driven or emotional eating dominant pattern. If the honest description of the eating pattern is snacking on highly palatable foods, evening grazing, or cravings that dominate over true hunger, Contrave’s naltrexone + bupropion mechanism targets the reward circuit more directly than the satiety-only mechanism in Qsymia and phentermine.
2. Comorbid depression. Bupropion is FDA-approved for major depressive disorder, so Contrave can serve double duty for the depressed patient who also needs weight-loss support. Bupropion is weight-neutral to modestly weight-lowering, unlike most SSRIs.
3. Patient wants once-a-day-progression titration and no controlled-substance status. Contrave is not DEA-scheduled, so there is no monthly-refill or state-database burden. The 4-week titration (one tablet, then two, then three, then four) is predictable and reversible if a step is not tolerated.

When Qsymia is the better answer

Three concrete cases where Qsymia is the better pick:

1. BMI ≥ 30 and a weight-loss goal above roughly 7%. Qsymia’s placebo-adjusted 9–11% at 56 weeks is the highest of the three — meaningfully above Contrave (~5%) and above what phentermine will produce at 12 weeks. If the target is above the Contrave ceiling, escalating to Qsymia is often the right next step rather than adding a second drug.
2. Comorbid migraine. Topiramate is an FDA-approved migraine prophylactic drug, and Qsymia 11.25/69 mg or 15/92 mg delivers topiramate in the therapeutic prophylaxis range. A Qsymia patient with chronic migraine often gets to discontinue a separate topiramate prescription.
3. Patient can tolerate paresthesia and mild cognitive dulling, and is not planning pregnancy. The Qsymia REMS teratogenicity architecture is a real burden — pregnancy testing at baseline and monthly, effective contraception, and immediate discontinuation on any positive test — but it is workable for the non-pregnant patient who is comfortable with the topiramate side-effect footprint.

When Phentermine alone is the better answer

Three concrete cases where phentermine monotherapy wins:

1. Cost is the primary constraint. Nothing else comes close to $15–$40/month cash-pay with no coupon needed. For the uninsured patient or the patient whose plan excludes obesity medications, phentermine is the practical starting drug.
2. Patient wants a short-term jumpstart on a defined 12-week plan. Phentermine is fast-acting, fatigue-forward on the mechanism, and often delivers visible weight change in the first month — useful as a behaviour-change catalyst around a defined lifestyle intervention. A planned 12-week course followed by transition to maintenance behaviours is a legitimate use case that the label explicitly supports.
3. T2D-negative, CV-history-negative, and patient wants monotherapy simplicity. Phentermine is one drug, one pill, one daily dose, one class of monitoring (BP and HR). For a straightforward patient with no relevant comorbidity, the simplicity is a feature rather than a limitation.

Frequently asked questions

Which is the most effective for weight loss: Contrave, Qsymia, or Phentermine? Qsymia is the strongest of the three on trial-controlled data. In CONQUER (Gadde 2011, Lancet, n=2,487, 56 weeks), top-dose Qsymia 15/92 mg produced roughly 9–11% placebo-adjusted weight loss. Contrave 32/360 mg produced about 5% placebo-adjusted loss in COR-I (Greenway 2010, Lancet, n=1,742, 56 weeks). Phentermine monotherapy produces roughly 5–10% weight loss at 12 weeks in most trials (dose- and duration-dependent), but has no controlled 56-week comparator because its FDA label is short-term only. Ranking at maximum tolerated dose over 12 months: Qsymia > Contrave ≈ Phentermine. None reaches semaglutide 2.4 mg (~15%) or tirzepatide 15 mg (~21%).

Which is the cheapest of the three in 2026? Phentermine is by far the cheapest. Generic phentermine hydrochloride 37.5 mg runs $15–$40 per month cash pay through pharmacy discount programs — no coupons or manufacturer program needed. Contrave brand runs about $99/month through the Currax direct-pay bundled coupon, or roughly $25/month with commercial insurance and prior authorization. Qsymia brand runs $200–$285/month through the Vivus Qsymia Advantage direct-pay program; commercial-insurance copay assist caps at $70. All three fail Medicare Part D’s obesity-drug exclusion, so seniors typically pay full cash unless they have secondary coverage that carves out obesity medications.

Which is safest? Safety depends heavily on the patient. Contrave carries a boxed warning for suicidal thoughts and behaviour (inherited from bupropion) and is contraindicated in patients on chronic opioids. Qsymia carries a REMS teratogenicity program (topiramate causes a 2- to 3-fold increased risk of first-trimester cleft palate) and is contraindicated in pregnancy. Phentermine has no boxed warning but is pregnancy category X, DEA Schedule IV, and contraindicated in coronary artery disease, uncontrolled hypertension, arrhythmias, and heart failure. There is no single-safest choice — each has a decision-driving contraindication that rules it out for a specific population. The right question is which safety profile is compatible with your history.

Can I take Phentermine long-term? Legally in the US, yes — off-label. The FDA label for phentermine is short-term (up to 12 weeks) and dates to a 1959 approval that has never been updated. There is no pharmacological reason phentermine cannot be used longer: Hendricks 2011 (Obesity) followed 269 patients on continuous phentermine for up to 21 months and found no tachyphylaxis, no cardiovascular safety signal, and durable weight loss. The 2016 AACE Obesity Clinical Practice Guideline and the 2022 ASBP position statement both endorse long-term off-label use with monitoring. Many US prescribers use phentermine chronically or in a 12-weeks-on / 4-weeks-off cycle. Insurance coverage, DEA prescribing conventions, and some state pharmacy boards still enforce the 12-week label, so it remains a clinician-judgement call rather than a routine one.

Do any of these three work as well as Ozempic, Wegovy, Zepbound, or Mounjaro? No. On trial-controlled 12-month weight loss, Qsymia (~10%) is the closest of the three, but semaglutide 2.4 mg (Wegovy at ~15% in Wilding 2021 STEP-1, NEJM) and tirzepatide 15 mg (Zepbound at ~21% in Jastreboff 2022 SURMOUNT-1, NEJM) both exceed it. Contrave and phentermine come in lower still, at roughly 5–7%. The honest framing: the three non-GLP-1 orals are meaningfully less effective than modern GLP-1 injectables. Their case for use in 2026 is cost, coverage denial for GLP-1s, GLP-1 contraindications (personal or family history of medullary thyroid cancer, active pancreatitis history), severe GI intolerance to the GLP-1 class, or a specific mechanistic fit — not head-to-head efficacy.

Can I use one of these three if GLP-1s made me too nauseated? Yes, and it is one of the most common reasons to reach for them. All three of Contrave, Qsymia, and Phentermine work through mechanisms unrelated to gastric emptying, so the delayed-gastric-emptying nausea that dominates GLP-1 tolerability does not carry over. Contrave still has meaningful nausea (~30% in COR trials) from bupropion, but the pattern is different from GLP-1 nausea. Qsymia and phentermine have low GI side-effect burdens; their tolerability issues sit elsewhere — cognitive dulling and paresthesia for Qsymia, insomnia and elevated heart rate for phentermine. See our guide on managing GLP-1 side effects for GI-adjunct strategies if you want to try to stay on a GLP-1 before switching class.

Which is the best choice if I have depression? Contrave, in most cases. The bupropion component of Contrave (naltrexone-bupropion) is itself an FDA-approved antidepressant for major depressive disorder, so Contrave can serve double duty for the depressed patient who also needs weight-loss support. Bupropion is one of the few antidepressants that is weight-neutral to modestly weight-lowering, unlike most SSRIs which can drive weight gain. Do note the boxed warning for suicidal thoughts in patients aged 24 and under, and screen mood carefully at baseline and follow-up. Phentermine can worsen anxiety and insomnia and is generally avoided in active anxiety or agitated depression. Qsymia has no direct antidepressant effect and can add cognitive dulling that some patients with depression find intolerable.

Which is the best choice if I have a history of migraine? Qsymia, because topiramate — its second active ingredient — is an FDA-approved migraine prophylactic drug in its own right. For the patient with obesity plus chronic migraine, Qsymia can serve double duty and often lets a separate topiramate prescription be discontinued. Practical dose note: Qsymia’s top dose 15/92 mg delivers 92 mg of extended-release topiramate daily, at the low end of the migraine-prophylaxis range (typically 100 mg/day). The mid-dose 11.25/69 mg is also in a therapeutic range for migraine. Contrave and phentermine offer no migraine-prophylactic benefit.