Most adults qualify for prescription weight loss medication with a BMI of 30 or higher, or a BMI of 27 or higher paired with a weight-related health condition like high blood pressure or type 2 diabetes. Those are the standard thresholds set by the FDA, and they apply across the major prescribed medications. But meeting the BMI cutoff is just the starting point. Your doctor, your insurance plan, and the specific medication all add layers to the qualification process.
The BMI Thresholds
BMI, or body mass index, is calculated from your height and weight. A BMI of 30 puts you in the “obesity” category, and at that level you’re generally eligible for any FDA-approved weight loss medication without needing an additional diagnosis. If your BMI falls between 27 and 29.9, you’ll need at least one weight-related comorbidity to qualify. The two most commonly referenced are high blood pressure and type 2 diabetes, but other conditions count too, including high cholesterol, obstructive sleep apnea, and heart disease.
For adolescents aged 12 to 17, the threshold is different. Instead of a fixed BMI number, obesity is defined as a BMI at or above the 95th percentile for their age and sex. In 2022, the FDA expanded approval of two major weight loss medications to include this age group, and the American Academy of Pediatrics now recommends offering medication to adolescents 12 and older with obesity alongside lifestyle changes.
What Your Doctor Will Look At
Before writing a prescription, your doctor will typically run bloodwork to get a baseline picture of your health and screen for conditions that might affect which medication is appropriate. Common panels include blood sugar (often measured as HbA1c, which reflects your average over two to three months), a cholesterol and lipid panel, kidney function markers, and liver enzymes. Thyroid testing is also standard, partly because an underactive thyroid can contribute to weight gain, and partly because certain medications carry thyroid-related warnings.
Your medical history matters as much as your lab results. GLP-1 medications, the class that includes the most widely prescribed newer options, are not safe during pregnancy. Animal studies have shown developmental harm to the fetus. People with a personal or family history of a rare type of thyroid cancer called medullary thyroid carcinoma are also typically excluded from these medications, since they carry a warning about that specific cancer risk. Some patients develop antibodies to GLP-1 drugs, which can reduce effectiveness or cause allergic reactions ranging from mild injection-site irritation to, in rare cases, severe anaphylaxis.
Insurance Coverage and Prior Authorization
This is where many people hit a wall. Even if you meet the medical criteria, your insurance plan may impose its own requirements before approving coverage. Prior authorization is standard for most weight loss medications, and the process varies widely between insurers.
A common requirement is documented evidence of lifestyle changes. Many plans want to see that you’ve spent at least six months trying diet and exercise modifications before they’ll approve medication. Some state Medicaid programs don’t cover GLP-1 medications for weight loss at all, covering them only for diabetes or other FDA-approved conditions. Pennsylvania’s Medicaid program, for example, explicitly excludes coverage of GLP-1 drugs for treating overweight or obesity, while covering the same drugs for other diagnoses like reducing cardiovascular risk or treating liver disease.
If your plan does cover weight loss medications, expect to provide documentation from your doctor that includes your BMI, any relevant comorbidities, lab results, and a record of prior weight management efforts. Some plans also require that prescriptions come from specific provider types or that you’re enrolled in a structured weight management program.
Staying on Medication: Renewal Criteria
Qualifying for a first prescription is one thing. Continuing to get refills is another. Most prescribers and insurance plans expect to see measurable progress within the first few months, and the benchmarks differ by medication.
- Semaglutide: 5% body weight loss after reaching the full maintenance dose, which takes roughly 20 weeks of gradual dose increases.
- Tirzepatide: 5% body weight loss after completing dose titration, which can take anywhere from 4 to 16 weeks depending on the target dose.
- Liraglutide: 4% body weight loss by week 16. If you haven’t hit that mark, the prescribing guidance recommends discontinuing because meaningful further loss is unlikely.
- Naltrexone/bupropion: 5% body weight loss by 12 weeks, with the same recommendation to stop if the goal isn’t met.
- Phentermine/topiramate: 3% loss at 12 weeks on the starting dose, then 5% loss at 12 weeks if moved to the higher dose. Failure to reach that second target triggers a taper and discontinuation.
- Orlistat: 3% body weight loss at 12 weeks.
For ongoing refills beyond the initial period, the general expectation is that you maintain at least two-thirds of your initial weight loss, or stay above 5% total loss from your starting weight. Some systems review this every six months. You won’t necessarily need to keep losing weight indefinitely, but you do need to show you’re holding onto the progress you’ve made.
A Shifting Medical Landscape
The way doctors think about obesity treatment is evolving. The American Association of Clinical Endocrinology released updated guidance in 2025 that reframes obesity as “Adiposity-Based Chronic Disease,” or ABCD. Under this framework, even people with obesity who haven’t yet developed complications (classified as stage 1) are considered to have a disease state that warrants treatment to prevent future problems. People who have developed complications like joint disease, sleep apnea, or metabolic issues fall into stages 2 or 3.
This shift matters because it pushes the medical establishment toward treating obesity earlier, before complications set in, rather than waiting until someone has already developed diabetes or heart disease. It also gives doctors more clinical justification to prescribe medications to patients who meet the BMI threshold but don’t yet have a qualifying comorbidity under older guidelines. How quickly insurance companies adopt this thinking is a separate question, but the direction of clinical consensus is clear: earlier intervention, broader access.
How to Prepare for Your Appointment
If you’re considering weight loss medication, you can speed up the process by arriving prepared. Know your BMI going in (any online calculator will give you a reasonable estimate from your height and weight). Bring a list of any weight-related health conditions you’ve been diagnosed with, along with medications you’re currently taking. If you’ve been making dietary changes or exercising, keep a record of what you’ve been doing and for how long, since your doctor may need to document this for insurance purposes.
Ask your doctor’s office ahead of time whether they’ll handle the prior authorization process or whether you’ll need to do some of the legwork yourself. Some clinics have staff dedicated to navigating insurance approvals, while others leave more of the follow-up to patients. If your insurance denies coverage, ask about the appeals process. Many initial denials are overturned when additional documentation is submitted, particularly if your doctor can provide detailed records of failed lifestyle interventions and worsening health markers.