The Weight Loss Drug Comparison Calculator provides a side-by-side analysis of all major anti-obesity medications currently available, including semaglutide (Wegovy/Ozempic), tirzepatide (Zepbound/Mounjaro), liraglutide (Saxenda), phentermine, phentermine-topiramate (Qsymia), naltrexone-bupropion (Contrave), and orlistat (Xenical/Alli). The calculator compares these medications across multiple dimensions: efficacy (percentage of body weight lost in clinical trials), cost (list price, typical insurance copay, and compounded alternatives), side effect profiles, dosing convenience, and mechanism of action. The anti-obesity medication landscape has transformed dramatically since 2021 with the approval of high-dose semaglutide and tirzepatide, which produce 15 to 22 percent body weight loss compared to 5 to 10 percent for older medications. However, these newer GLP-1-based drugs are also dramatically more expensive ($900 to $1,350 per month versus $30 to $200 per month for older agents), creating a complex cost-effectiveness decision. For some patients, an older, less effective but more affordable medication may be the practical choice, while others may benefit from the superior efficacy of newer agents. The calculator is designed for patients deciding between medication options with their physician, for obesity medicine specialists comparing treatment pathways for individual patients, and for payers evaluating formulary placement and step-therapy protocols. It moves beyond simple efficacy rankings to incorporate patient-specific factors like comorbidities (certain medications have cardiovascular benefits while others are contraindicated with heart disease), prior medication trials (insurance may require step therapy through older agents before approving GLP-1 drugs), and practical considerations like injection versus oral dosing. By presenting all available data in a standardized comparison framework, this calculator helps ensure that treatment selection is based on evidence rather than marketing, and that patients understand the full range of options rather than only the most heavily advertised newer medications.
Comparison Score = (Efficacy Weight x %BWL / Max%BWL x 100) + (Cost Weight x (1 - Monthly Cost / Max Cost) x 100) + (Tolerability Weight x (1 - Side Effect Rate / Max Side Effect Rate) x 100) + (Convenience Weight x Dosing Score), where weights are user-adjustable and sum to 1.0. Default weights: Efficacy = 0.40, Cost = 0.25, Tolerability = 0.20, Convenience = 0.15. For a worked example comparing semaglutide 2.4 mg vs phentermine-topiramate: Semaglutide scores (0.40 x 14.9/20.9 x 100) + (0.25 x (1 - 1349/1349) x 100) + (0.20 x (1 - 0.44/0.44) x 100) + (0.15 x 80) = 28.5 + 0 + 0 + 12 = 40.5. Phentermine-topiramate scores (0.40 x 9.8/20.9 x 100) + (0.25 x (1 - 200/1349) x 100) + (0.20 x (1 - 0.20/0.44) x 100) + (0.15 x 100) = 18.8 + 21.3 + 10.9 + 15 = 66.0.
- 1Select two to six medications you want to compare from the available list. The calculator includes all FDA-approved anti-obesity medications and commonly used off-label options. You can select specific dose levels for dose-dependent medications (such as tirzepatide 5 mg versus 15 mg or semaglutide 1.0 mg versus 2.4 mg). Pre-built comparison sets are available for common scenarios: 'All GLP-1 drugs,' 'Budget-friendly options,' 'Oral medications only,' and 'Maximum efficacy options.'
- 2Adjust the priority weights to reflect what matters most to you. The default weighting emphasizes efficacy (40 percent) but some patients prioritize cost (if paying out of pocket), tolerability (if they have a history of medication side effects), or convenience (if they prefer oral medications over injections). Adjusting these weights changes the overall comparison score and may change which medication ranks highest for your individual priorities.
- 3Review the efficacy comparison showing mean percentage body weight loss from pivotal clinical trials. All data is sourced from the highest-quality randomized controlled trial for each medication. The calculator notes important caveats: trials had different durations (56 to 72 weeks), different patient populations, and different lifestyle intervention components, so direct head-to-head comparisons between non-GLP-1 and GLP-1 medications should be interpreted with caution. Only the SURMOUNT-5 trial directly compared tirzepatide to semaglutide.
- 4Examine the cost comparison showing list price, typical insured copay, cash price, and compounded alternatives where available. Cost data is updated quarterly and reflects US pricing. The calculator also shows the cost per percentage point of body weight lost, which normalizes the cost comparison by efficacy. For example, if medication A costs $200 per month and produces 10 percent weight loss, its cost per percentage point is $20/month, while medication B at $1,000 per month producing 20 percent weight loss has a cost per percentage point of $50/month.
- 5Review the side effect comparison using a standardized format showing the incidence rate for each major side effect category: gastrointestinal (nausea, vomiting, diarrhea, constipation), cardiovascular (heart rate increase, blood pressure changes), neurological (dizziness, headache, insomnia), and other (dry mouth, altered taste, oily stools). The calculator highlights any black box warnings, absolute contraindications, and serious adverse events for each medication.
- 6The practical considerations comparison covers dosing schedule (daily oral, weekly injection, twice-daily oral), injection site options, storage requirements (refrigeration versus room temperature), availability and supply status, and typical insurance coverage rates. For many patients, the practical differences between a once-weekly injection and a twice-daily pill significantly influence their preference and adherence likelihood.
- 7Generate a personalized recommendation based on your weights, comorbidities, prior medication trials, and insurance coverage. The calculator produces a ranked list with a brief rationale for each medication's position. The recommendation should be discussed with your healthcare provider, who can factor in clinical judgment, your complete medical history, and current prescribing guidelines.
When efficacy is heavily weighted, tirzepatide dominates due to its 20.9 percent body weight loss versus 14.9 percent for semaglutide and 8.0 percent for liraglutide. However, all three require injectable administration and have similar cost profiles, so patients who prioritize efficacy above all else should discuss tirzepatide with their provider.
For cost-conscious patients, phentermine-topiramate offers the best efficacy-to-cost ratio at approximately $150 to $250 per month for 9.8 percent body weight loss. Over-the-counter orlistat is the cheapest option at about $50 per month but produces only 3 to 5 percent weight loss.
For patients who prefer pills over injections, oral semaglutide at the 50 mg dose (approved in 2024 for weight management) produces approximately 15 percent body weight loss, comparable to injectable Wegovy. Phentermine-topiramate remains a strong oral option at lower cost but with cardiovascular contraindications that limit its use in some patients.
Obesity medicine specialists use structured comparison tools during shared decision-making conversations with patients. Rather than simply recommending the most effective medication, specialists present the full comparison including cost, side effects, and practical considerations, empowering patients to make informed choices aligned with their values and circumstances. This approach improves patient satisfaction and medication adherence because patients feel ownership over their treatment decision.
Insurance formulary committees use comparative effectiveness data to design step-therapy protocols that balance clinical benefit with cost management. A typical step-therapy design might require patients to try phentermine or naltrexone-bupropion (lower cost, moderate efficacy) for 3 to 6 months before approving a GLP-1 medication (higher cost, higher efficacy). The comparison data helps determine whether these step-therapy barriers are clinically reasonable or counterproductive.
Pharmacy benefit managers use drug comparison frameworks to negotiate pricing with pharmaceutical manufacturers. By demonstrating that competing medications in the same class produce similar outcomes (such as semaglutide versus tirzepatide), PBMs can negotiate volume-based rebates by threatening to move preferred status from one drug to the other. The comparison data quantifies how substitutable these medications are for the average patient.
Health economics researchers use standardized drug comparisons to calculate quality-adjusted life year (QALY) gains per dollar spent on each medication, which informs national health technology assessments. These analyses determine whether the incremental efficacy of newer, more expensive medications justifies their cost premium relative to older, cheaper alternatives from a societal resource allocation perspective.
Patients with cardiovascular disease face important contraindications that narrow their medication options.
Phentermine and phentermine-topiramate are contraindicated in patients with uncontrolled hypertension, coronary artery disease, or arrhythmias due to their sympathomimetic effects. Conversely, semaglutide 2.4 mg has demonstrated a 20 percent reduction in major adverse cardiovascular events in the SELECT trial, making it the preferred option for patients with obesity and established cardiovascular disease. The drug comparison for this patient population is fundamentally different from the general obesity population.
Patients with a history of eating disorders, particularly binge eating disorder
Patients with a history of eating disorders, particularly binge eating disorder or bulimia nervosa, require careful medication selection. Naltrexone-bupropion is specifically contraindicated in patients with bulimia or anorexia nervosa. Phentermine, as a stimulant, may exacerbate restrictive eating patterns. GLP-1 medications reduce appetite through physiological mechanisms rather than stimulant effects and are generally considered safer in this population, though any weight loss medication should be prescribed in conjunction with eating disorder treatment.
Patients who are already taking psychiatric medications face potential drug
Patients who are already taking psychiatric medications face potential drug interactions that affect medication selection. Bupropion (a component of Contrave) interacts with MAO inhibitors and medications that lower the seizure threshold. Topiramate (a component of Qsymia) can reduce the effectiveness of hormonal contraceptives. GLP-1 medications have relatively few drug-drug interactions but can slow gastric emptying, potentially affecting the absorption of oral medications. The calculator flags relevant interactions based on the patient's current medication list.
| Medication | Route | Mean %BWL | Monthly Cost (list) | Key Side Effects | CV Benefit |
|---|---|---|---|---|---|
| Tirzepatide 15 mg (Zepbound) | Weekly injection | 20.9% | $1,060 | Nausea, diarrhea | Under study |
| Semaglutide 2.4 mg (Wegovy) | Weekly injection | 14.9% | $1,349 | Nausea, vomiting | Yes (SELECT trial) |
| Oral semaglutide 50 mg | Daily oral | ~15% | $1,000+ | Nausea, diarrhea | Likely (extrapolated) |
| Liraglutide 3.0 mg (Saxenda) | Daily injection | 8.0% | $1,349 | Nausea, vomiting | Neutral |
| Phentermine-topiramate (Qsymia) | Daily oral | 9.8% | $150-250 | Dry mouth, paresthesia | Contraindicated in CVD |
| Naltrexone-bupropion (Contrave) | Twice daily oral | 6-8% | $100-200 | Nausea, headache | Neutral |
| Orlistat (Xenical) | Three times daily oral | 3-5% | $50-100 | Oily stools, flatulence | Neutral |
| Phentermine (generic) | Daily oral | 5-7% | $15-40 | Insomnia, dry mouth | Contraindicated in CVD |
What is the most effective weight loss medication available?
As of 2025, tirzepatide 15 mg (Zepbound/Mounjaro) produces the highest mean body weight loss of any FDA-approved medication at 20.9 percent over 72 weeks in the SURMOUNT-1 trial. The head-to-head SURMOUNT-5 trial confirmed tirzepatide's superiority over semaglutide 2.4 mg, showing 20.2 percent versus 13.7 percent body weight loss. However, individual responses vary substantially, and some patients respond better to semaglutide than tirzepatide. The most effective medication is the one that produces the best result for a specific patient while being tolerable, affordable, and accessible.
What is the cheapest weight loss medication that actually works?
Generic phentermine is the lowest-cost prescription weight loss medication at approximately $15 to $40 per month, producing about 5 to 7 percent body weight loss. Phentermine-topiramate (Qsymia) costs $150 to $250 per month and produces approximately 9.8 percent body weight loss, offering the best efficacy-to-cost ratio among non-GLP-1 medications. Over-the-counter orlistat (Alli) costs about $50 per month but produces only 3 to 5 percent additional weight loss and has unpleasant gastrointestinal side effects. Compounded semaglutide at $150 to $300 per month offers GLP-1-level efficacy at a fraction of brand-name cost.
Are there any weight loss medications that do not require injections?
Yes, several effective oral options exist. Phentermine-topiramate (Qsymia) is an oral daily medication producing approximately 9.8 percent weight loss. Naltrexone-bupropion (Contrave) is an oral twice-daily medication producing approximately 6 to 8 percent weight loss. Oral semaglutide at higher doses (50 mg) was approved for weight management and produces results comparable to injectable semaglutide. Orlistat (Xenical/Alli) is available both by prescription and over-the-counter. Phentermine alone is an oral option for short-term use (up to 12 weeks by original labeling, though many physicians prescribe it longer).
Can I combine weight loss medications for better results?
Combination therapy is an area of active research. Currently, the FDA-approved combination of phentermine plus topiramate (marketed as Qsymia) is the only approved fixed-dose combination for obesity. Some physicians prescribe GLP-1 medications alongside phentermine or naltrexone-bupropion off-label, and early evidence suggests these combinations may produce additive benefits. However, combining medications increases cost, side effect risk, and complexity, and the safety data for most combinations is limited. Always discuss combination approaches with your physician rather than self-combining medications.
How long do I need to take weight loss medication?
For GLP-1 medications (semaglutide, tirzepatide, liraglutide), current evidence strongly suggests that treatment must be continued indefinitely to maintain weight loss. The STEP 1 extension trial showed that two-thirds of weight lost on semaglutide was regained within one year of stopping. Older medications have similar patterns. Obesity is increasingly understood as a chronic disease requiring ongoing management, similar to hypertension or diabetes, rather than a condition that can be treated for a defined period and then cured. The duration-of-treatment question is one of the most important factors in long-term cost calculations.
Pro Tip
When comparing medications with your physician, bring a list of your priorities ranked in order of importance to you. If cost is your primary constraint, the conversation will be very different than if maximum efficacy is your goal. Also ask about your insurance plan's step-therapy requirements, because even if you and your physician agree that a GLP-1 medication is the best option, your insurance may require you to try a less expensive medication first for 3 to 6 months before approving coverage.
Did you know?
Before the GLP-1 era, the most effective anti-obesity medication ever marketed was fenfluramine-phentermine (fen-phen), which was withdrawn in 1997 after causing fatal heart valve disease in some patients. The fen-phen crisis led to decades of extreme caution in anti-obesity drug development and created a stigma around weight loss medications that persisted until semaglutide demonstrated both safety and unprecedented efficacy in the STEP trials.