Medically reviewed by
Betsy Greenleaf, DO
Board-Certified OB/GYN & Urogynecologist; Empire Director of Anti-Aging For most of the last century, the medical weight loss conversation was narrow: a stimulant appetite suppressant for a few weeks, and not much else. That era is over. The clinician treating obesity today has a genuine toolbox — several distinct drug classes, each acting on a different part of the physiology that drives weight, and each with its own evidence base, safety profile, and place in therapy. This page is the hub that maps that toolbox and links out to a dedicated overview of each agent.
One framing should anchor everything that follows. As Dr. Betsy Greenleaf teaches in Empire's medical weight loss course, obesity is a chronic, relapsing, multifactorial disease — not a failure of willpower and not a cosmetic complaint. Medications are tools for managing that disease; they are not a substitute for the diet, physical activity, and behavior change that remain the foundation of every weight-management plan. This guide is clinical education, not medical advice, and nothing here is a protocol or a recommendation for an individual patient. It sits within Empire's broader medical weight loss resource center.
When pharmacotherapy is indicated
Pharmacotherapy enters the picture when lifestyle measures alone have not produced or sustained adequate results in a patient whose weight is a genuine health concern. The conventional eligibility framing is anchored to body mass index: broadly, a BMI of 30 or higher, or a BMI of 27 or higher in the presence of at least one weight-related comorbidity such as hypertension, type 2 diabetes, dyslipidemia, or obstructive sleep apnea. BMI is easy to measure, inexpensive, standardized, and strongly correlated with body-fat-related risk at the population level — which is why it remains the screening tool of record.
It is also, as Dr. Greenleaf is careful to point out, an imperfect measurement. BMI does not distinguish lean mass from fat mass, is a weaker predictor of body fat in the elderly than in younger adults, and at the same BMI women on average carry more body fat than men. The practical conclusion is that the BMI thresholds are a starting point for the conversation, not a verdict — they are interpreted alongside waist circumference, comorbidity burden, and the individual clinical picture. The specific eligibility logic and drug-by-drug labeling are taught in depth in Empire's training rather than reduced to a number on a page.
Appetite suppressants
Phentermine is the oldest and most commonly prescribed appetite suppressant, and it remains a reasonable first-line agent for the right patient. It is a stimulant in the sympathomimetic amine class: by raising levels of norepinephrine, and to a lesser degree serotonin and dopamine, it reduces hunger, and it also modestly increases energy expenditure. Trial data put the average weight loss in the range of roughly 3% of initial body weight at three months and 5–7% at six months.
Because it is a stimulant, the relevant cautions are cardiovascular — it raises heart rate and blood pressure — and it is a schedule IV controlled substance approved for short-term use. That short-term labeling is a large part of why the field moved toward combination products and longer-acting agents. For the full mechanism, evidence, contraindications, and how providers actually use it, see the dedicated phentermine overview.
Combination agents
Pairing two drugs with complementary mechanisms can deliver more weight loss than either alone while keeping individual doses lower. Two FDA-approved oral combinations dominate this category.
Phentermine-topiramate (Qsymia)
Phentermine-topiramate, marketed as Qsymia, joins the appetite suppression of phentermine with topiramate, an agent that further blunts appetite and is also used in binge-eating contexts. The combination consistently outperforms phentermine alone on average weight loss, which is why it became an attractive option once short-term phentermine monotherapy hit its ceiling. It carries class cautions around the stimulant component and topiramate-specific considerations that providers screen for, particularly in patients who may become pregnant. Read the full profile on the phentermine-topiramate overview.
Bupropion-naltrexone (Contrave)
Bupropion-naltrexone, marketed as Contrave, works through a different and clinically interesting pathway. Bupropion influences the brain's appetite-regulation centers and acts on noradrenaline and dopamine; naltrexone, an opioid antagonist, modulates the brain's reward centers. Together they target a population that older appetite suppressants miss: patients whose eating is reward-driven or emotional rather than simply hunger-driven. Studies show roughly a 5–11.5% reduction in weight, with the larger figures seen when the drug is paired with intensive diet and lifestyle change. It carries a boxed warning regarding suicidal behavior in patients with psychiatric conditions, which makes patient selection central. See the full bupropion-naltrexone overview.
GLP-1 and dual-incretin receptor agonists
The agents that reshaped the field are the incretin-based injectables. Semaglutide is a GLP-1 receptor agonist; tirzepatide is a dual agonist acting on both GLP-1 and GIP receptors. Both reduce appetite by activating GLP-1 receptors in the brain, slow gastric emptying to prolong fullness, and improve glycemic control — and in trials they have produced the largest average weight loss of any class, generally well into the double digits as a percentage of body weight.
Their evidence base, dosing logic, and side-effect management are deep enough to warrant their own coverage. Start with the GLP-1 medications for weight loss overview for the class-level clinical picture. For molecule-level detail — mechanism, FDA-approved brands, the STEP and SELECT trial evidence, and the compounding question — see the peptide-cluster guides to semaglutide and tirzepatide.
Other and off-label agents
Several additional medications are used in weight management, some on label and some off label. This is a good place to note the regulatory reality Dr. Greenleaf emphasizes: the FDA does not dictate how an approved drug may be prescribed. Once a product is approved for marketing, a physician may use it off label in the exercise of clinical judgment — a long-standing principle, but one that carries responsibility to understand the evidence and document the rationale.
- Metformin (off-label) — an insulin-sensitizing agent in use since the 1950s for diabetes and PCOS. It supports modest weight loss, generally in the 2–5% range, by reducing appetite, influencing gut microbiota, and acting on appetite-regulating signals. It is particularly relevant in patients with insulin resistance, and its long safety record makes it a low-risk adjunct in the right context.
- Orlistat — an FDA-approved lipase inhibitor (approved 1997) that blocks the breakdown and absorption of dietary fat in the gut, with roughly 10% weight loss at one year. Its mechanism is also its limitation: gastrointestinal effects such as bloating, oily stool, and fecal incontinence drive frequent discontinuation, and it carries a warning following rare reports of severe liver injury. Fat-soluble vitamin supplementation is needed.
Injectable adjuncts
A separate category of injectables is used as supportive adjuncts rather than primary anti-obesity drugs, and honesty about the evidence matters here.
MIC / lipotropic injections
MIC and lipotropic injections combine compounds such as methionine, inositol, and choline, often with B vitamins. The rationale is biochemical: choline-derived agents like betaine act as methyl-group donors in the liver's methionine cycle, supporting fat metabolism, raising glutathione, and lowering homocysteine. These injections are positioned as metabolic support alongside a diet-and-exercise program, not as standalone weight-loss drugs. See the dedicated MIC/lipotropic injections overview for what the evidence does and does not support.
HCG
HCG for weight loss warrants a clear-eyed read. The historical HCG protocol pairs the hormone with a very-low-calorie diet, and the controlled evidence is unfavorable: meta-analyses have been negative, and the FDA has stated that HCG has not been demonstrated to be an effective adjunct for obesity, with no evidence that it increases weight loss beyond caloric restriction or reduces hunger. Any weight lost on these protocols is attributable to the severe calorie restriction, which carries its own risks. Providers should understand this evidence before offering it; the full picture is in the HCG for weight loss overview.
How to choose among them
There is no single “best” weight loss drug — there is a best match for a given patient. The GLP-1 and dual-incretin agonists win on average trial efficacy, but choosing well means weighing several variables at once:
- Comorbidities — type 2 diabetes or established cardiovascular disease points toward an incretin agonist; insulin resistance or PCOS may favor metformin as an adjunct.
- Eating pattern — reward-driven or emotional eating is the specific niche bupropion-naltrexone was built for.
- Contraindications — cardiovascular risk limits the stimulants; a personal or family history of medullary thyroid carcinoma rules out GLP-1 agonists; psychiatric history shapes the bupropion-naltrexone decision.
- Tolerability, cost, and route — injectable versus oral, GI burden, and price all affect whether a patient actually stays on therapy, and adherence is what ultimately determines outcome.
Two principles cut across the entire toolbox. First, the medication is an adjunct, and the lifestyle program underneath it is what makes it work. Second, lean-mass preservation is the often-missed half of the job: a meaningful fraction of weight lost on any aggressive regimen can be muscle rather than fat, which is the opposite of the metabolic goal — so adequate protein intake and resistance training should travel with every prescription. Dr. Greenleaf also cautions that excessive or overly strenuous exercise can register as a stressor and stall weight loss, so the recommendation is sustained, moderate activity rather than punishing workouts.
Monitoring and safety
Each class brings its own surveillance requirements, but the structure is consistent. A baseline assessment establishes pretreatment status — blood pressure, resting heart rate, glucose and insulin, lipids, and relevant labs — and screens for the contraindications specific to the chosen agent. An early follow-up focuses on tolerability and, for stimulants, on cardiovascular parameters. Periodic reassessment then judges efficacy against expectations.
One pragmatic rule Dr. Greenleaf returns to: across many of these medications, if no meaningful weight loss is seen, the medication is stopped rather than continued indefinitely. Drug-specific safety flags — the boxed warning on bupropion-naltrexone, the liver-injury caution and vitamin depletion with orlistat, the cardiovascular ceiling on stimulants, and the GI and thyroid C-cell considerations with GLP-1 agonists — all sit on top of this shared monitoring backbone. Specific dosing, titration schedules, and exact incidence figures belong to current FDA labeling and individualized clinical judgment, and are taught in Empire's course rather than published as a protocol here.
Master the full weight loss toolbox
Empire Medical Training's Physician Medical Weight Loss Training is a CME-accredited course covering obesity as a chronic disease, every medication class on this page, patient selection and monitoring, lean-mass preservation, and how to build a compliant, profitable weight-management practice — developed and taught by Dr. Betsy Greenleaf, DO. Available in person and via livestream.
Explore the Medical Weight Loss Training →Weight loss medications: frequently asked questions
What medications are used for weight loss?
The medical weight loss toolbox spans several drug classes: appetite suppressants such as phentermine; combination agents such as phentermine-topiramate (Qsymia) and bupropion-naltrexone (Contrave); GLP-1 and dual-incretin receptor agonists such as semaglutide and tirzepatide; off-label options such as metformin and the lipase inhibitor orlistat; and injectable adjuncts such as MIC/lipotropic injections. Each works by a different mechanism, and choice depends on the patient. All are intended as adjuncts to diet, physical activity, and behavior change rather than replacements for them.
Who qualifies for weight loss medication?
Pharmacotherapy is generally considered for adults with a BMI of 30 or higher, or a BMI of 27 or higher with at least one weight-related comorbidity such as hypertension, type 2 diabetes, dyslipidemia, or obstructive sleep apnea, after lifestyle measures alone have proven insufficient. BMI is an imperfect screening tool, so it is interpreted alongside the individual clinical picture. Exact eligibility, contraindications, and drug-specific labeling are part of structured provider training.
Which weight loss drug is most effective?
In clinical trials the GLP-1 and dual-incretin receptor agonists, semaglutide and tirzepatide, have produced the largest average weight loss, generally well into the double digits as a percentage of body weight, exceeding older agents such as phentermine or orlistat. However, the most effective drug for a given patient depends on comorbidities, tolerability, contraindications, cost, and adherence, so the highest trial average is not automatically the right choice for every individual.
Are weight loss medications safe?
Approved weight loss medications have defined and generally manageable safety profiles when prescribed appropriately, but each carries specific risks. Stimulant appetite suppressants raise blood pressure and heart rate; bupropion-naltrexone and orlistat carry boxed or serious warnings; GLP-1 agonists cause gastrointestinal effects and carry a thyroid C-cell tumor warning. Safe use depends on proper patient selection, screening for contraindications, and monitoring by a qualified prescriber working from current FDA labeling.
What training do providers need to prescribe them?
Most weight loss medications can be prescribed by any licensed prescriber, but using them well requires understanding obesity as a chronic disease, the mechanism and evidence behind each drug class, patient selection and contraindications, dose escalation, side-effect management, and lean-mass preservation. Empire Medical Training offers a CME-accredited physician medical weight loss training course that covers the full medication toolbox in clinical depth.
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