Weight Loss Medications Explained: GLP-1s, How They Work, and What to Expect

The Short Answer

Medical weight loss mostly means GLP-1 receptor agonists — the class that includes Ozempic, Wegovy, Mounjaro and Zepbound. They work by regulating appetite hormones rather than "burning fat," they produce meaningful weight loss for most people who stay on them, and they come with real side effects and real tradeoffs worth understanding before you commit.

Two of them are now pills. Novo's oral semaglutide is sold as a Wegovy tablet, and on April 1, 2026 the FDA approved Lilly's Foundayo (orforglipron) — the first GLP-1 pill that can be taken any time of day with no food or water restrictions. If the weekly injection has been the thing stopping you, that objection is gone.

Older medications like phentermine and metformin still have a place, usually as lower-cost options. Here's how the landscape actually breaks down.

***

What GLP-1s Are and How They Work

GLP-1 stands for glucagon-like peptide-1, a hormone your gut naturally releases after you eat. It's part of a family of signaling hormones called incretins, which tell your body "food has arrived" — prompting insulin release, slowing digestion, and signaling fullness to your brain.

GLP-1 medications are lab-made versions of this hormone (technically, they're peptides — see our Peptide Therapies Explained guide for how they fit into that broader category). They're engineered to last days instead of minutes, which is why most are a once-weekly injection. Three effects drive the weight loss:

• Appetite regulation. GLP-1s act on appetite centers in the brain, reducing hunger and quieting "food noise" — the constant background pull toward eating that many patients describe.
• Slower gastric emptying. Food leaves your stomach more slowly, so you feel full sooner and stay full longer on smaller portions.
• Better blood sugar control. GLP-1s prompt insulin release only when glucose is elevated, which is why the class was originally developed for Type 2 diabetes.

The net effect: most people simply eat less without the white-knuckle willpower that makes traditional dieting fail.

***

The Main GLP-1 Medications

A few things worth knowing:

• Liraglutide is the older option — a daily rather than weekly injection, with generally more modest weight loss. It's mostly relevant today when cost or availability rules out the newer drugs.
• Semaglutide is the most widely prescribed and most studied option. Ozempic and Wegovy contain the same active ingredient — the difference is the approved use and maximum dose.
• Tirzepatide activates a second incretin receptor (GIP) alongside GLP-1. In head-to-head and cross-trial comparisons, it has produced greater average weight loss than semaglutide, though individual response varies widely.
• Orforglipron is the newest and the first of a different kind: a small-molecule GLP-1 rather than a peptide, which is why it survives digestion and can be taken as an ordinary tablet without the food and water timing rules that oral semaglutide requires. In Lilly's ATTAIN-1 trial, people on the highest dose who stayed on treatment lost an average of 27.3 pounds, or 12.4% of body weight, against 2.2 pounds on placebo. That is meaningful but below what the top injectable doses have produced, so the pill is a convenience trade rather than a straight upgrade.

***

Brand-Name vs. Compounded

Both semaglutide and tirzepatide exist as brand-name products from the original manufacturers and have been sold as compounded versions made by compounding pharmacies. Compounded versions are intended to contain the same active ingredient, but they are not FDA-approved: the FDA has warned that some compounded products use different salt forms of the drug, and their potency and purity are not verified the way approved products are. The regulatory picture also changed recently — after the FDA declared the brand-name shortages resolved in 2024–2025, compounding pharmacies were required to stop producing routine copies, and products still marketed today occupy a contested legal gray zone.

The picture has moved further since. On April 30, 2026 the FDA proposed excluding semaglutide, tirzepatide and liraglutide from the 503B bulks list on the grounds that there is "no clinical need" for outsourcing facilities to compound them. And in March 2026 the FDA sent warning letters to 30 telehealth companies over how they market compounded GLP-1s, objecting to "claims implying sameness with FDA-approved products" and to firms "obscuring product sourcing by advertising drug products branded with the telehealth firm's name." No companies were named in that announcement.

The price argument for compounded has also weakened a lot. It used to be the difference between roughly $200 and roughly $1,200 a month. Today the manufacturers sell direct: Wegovy at $349 a month for standard doses, Zepbound vials at $299 to $449, and Foundayo from $149 for the lowest dose. A compounded route through a telehealth membership can still land near $139 a month all-in — genuinely cheaper, but by tens of dollars rather than by a factor of six, and without the FDA approval.

We won't duplicate the full numbers here — our GLP-1 Price Guide covers brand versus compounded pricing, insurance coverage, the Medicare GLP-1 Bridge and manufacturer savings programs in detail. The short version: run the comparison yourself before assuming compounded wins, and ask any provider which pharmacy fills your prescription and on what basis.

***

Older, Non-GLP-1 Options

GLP-1s get the headlines, but they're not the only tools. These older medications cost far less and still work for some people:

Average weight loss with these options is considerably smaller than with GLP-1s, but for the right patient — or the right budget — they remain legitimate choices a good clinic will discuss rather than skip.

***

Side Effects: The Honest Version

The common ones are gastrointestinal. Nausea is the most frequent, especially in the first weeks and after dose increases. Vomiting, constipation, diarrhea, and reflux are also common. For most people these are worst early on and fade as the body adjusts — slow dose titration exists specifically to manage this. Some people find them intolerable and stop; that's a real outcome, not a failure.

The serious ones are rare but worth knowing:

• Pancreatitis (inflammation of the pancreas) has been reported. Severe, persistent abdominal pain is a go-to-the-doctor symptom, not a wait-and-see one.
• Gallbladder problems, including gallstones, occur at somewhat higher rates — partly a known effect of rapid weight loss itself.
• Thyroid C-cell tumors were observed in rodent studies, and GLP-1 labels carry a boxed warning as a result. It's not established that this risk applies to humans, but people with a personal or family history of medullary thyroid carcinoma or MEN 2 syndrome should not take these medications.
• Not for use during pregnancy. GLP-1s should not be taken while pregnant or trying to conceive — the Wegovy label advises stopping at least two months before a planned pregnancy. Tirzepatide may also reduce the effectiveness of oral contraceptives around dose increases, so discuss contraception and conception timing with your prescriber.

A trustworthy provider will walk you through this list unprompted and screen your history before prescribing. One that glosses over it is a red flag.

***

Who Typically Qualifies

The standard criteria, drawn from the FDA labeling for weight-management GLP-1s:

• BMI of 30 or higher, or
• BMI of 27 or higher with at least one weight-related condition (high blood pressure, Type 2 diabetes, sleep apnea, high cholesterol)

Some cash-pay clinics apply these thresholds loosely. A clinic that will prescribe to anyone with a credit card is optimizing for revenue, not for you.

***

What a Realistic Treatment Arc Looks Like

Months 1–4: Titration. You start at a low dose and step up every four weeks or so. This is deliberate — it minimizes GI side effects. Weight loss is usually modest early on and accelerates as you reach higher doses.

Months 4–12: The working phase. This is where most of the weight loss happens. Clinical trials of semaglutide and tirzepatide ran 68–72 weeks, and participants lost weight steadily through most of that period.

The plateau. Everyone plateaus eventually. Your body adapts, and weight stabilizes at a new set point. A plateau after significant loss is the medication working, not failing.

Maintenance. Obesity behaves like a chronic condition, and these medications treat it rather than cure it. Some patients stay on a full or reduced dose long-term; some taper off with intensive lifestyle support.

The regain risk. This is the part too many clinics soft-pedal: in extension studies, people who stopped semaglutide regained, on average, the majority of the weight they had lost within a year. Appetite returns when the medication stops. Go in with a long-term plan — and a budget that assumes more than a six-month commitment.

***

Next Steps

• Estimate your real monthly cost with our GLP-1 cost calculator
• Learn what separates good providers from bad ones in How to Choose a GLP-1 Clinic
• Browse weight loss clinics near you to compare local and online options

***

Sources

• FDA — FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize — shortage resolution dates (tirzepatide December 19, 2024; semaglutide February 21, 2025) and compounder wind-down deadlines.
• FDA — FDA Proposes to Exclude Semaglutide, Tirzepatide, and Liraglutide on 503B Bulks List — April 30, 2026.
• FDA — FDA warns 30 telehealth companies against illegal marketing of compounded GLP-1s — March 3, 2026.
• Eli Lilly — FDA approves Foundayo (orforglipron) — April 1, 2026, approval, dosing and the ATTAIN-1 results quoted above.
• Novo Nordisk / NovoCare — Wegovy self-pay price guide (PDF) — injection and tablet pricing.
• Eli Lilly — Lilly lowers the price of Zepbound single-dose vials — December 1, 2025.
• Side effect, boxed warning, pregnancy and BMI-criteria statements are drawn from the FDA prescribing information for the medications named.

_Every dated claim above was verified against the source linked beside it on the date shown at the top of this guide. This guide is for information only and is not medical advice. Talk to a licensed clinician before starting or changing any treatment._