GLP-1 Medications: What These Drugs Actually Do, Who They Help, and What I Tell My Patients

I have spent over a decade in obstetrics and gynecology, and no class of drugs has reshaped my patient conversations like GLP-1 receptor agonists. Women come in asking about Ozempic for weight loss, whether Wegovy will affect their fertility, whether Mounjaro is safe while breastfeeding. Some have PMOS (the condition formerly called PCOS) and heard from a friend that a weight-loss shot fixed someone's irregular periods.

The questions are good. The information circulating online is a mess. What follows is what I actually tell patients, with the evidence behind it.

What GLP-1 is

GLP-1 stands for glucagon-like peptide-1, a hormone your body already makes. When you eat, L-cells in the lining of your small intestine release it into the bloodstream. It prompts the pancreas to secrete insulin, suppresses glucagon, slows gastric emptying so food stays in the stomach longer, and acts on receptors in the hypothalamus and brainstem to reduce appetite.¹

Natural GLP-1 is short-lived. An enzyme called DPP-4 degrades it within about two minutes.¹ That works fine until the metabolic system is compromised by insulin resistance or obesity, at which point the brief hormonal signal is no longer enough.

How the drugs work

GLP-1 receptor agonists are engineered versions of the hormone that resist DPP-4 breakdown. Injectable semaglutide stays active for roughly a week rather than two minutes, so the appetite suppression, insulin stimulation, and gastric slowing continue around the clock.

Patients describe the appetite effect as food occupying less mental space. They stop thinking about the next meal compulsively. Slowed gastric emptying keeps them full on less food, which is also why nausea is the most common early complaint: we are deliberately slowing a system accustomed to a certain pace.

Insulin secretion is stimulated in a glucose-dependent way, meaning the drug pushes insulin when blood sugar is high and backs off when it falls. Unlike sulfonylureas, GLP-1 agonists rarely cause hypoglycemia on their own.¹

The benefits extend well past weight. In the SELECT trial, 17,604 patients with obesity and established cardiovascular disease but no diabetes were followed for a mean of 39.8 months. Semaglutide reduced major adverse cardiovascular events by 20 percent.² That result moved these drugs out of the weight-loss category and into cardiometabolic medicine.

The FDA-approved GLP-1 medications

Two clarifications I repeat constantly. Mounjaro and Zepbound both contain tirzepatide, which is technically a dual GIP/GLP-1 agonist; it is grouped with this class because it activates the GLP-1 receptor and produces comparable clinical effects. Metformin is not a GLP-1 agonist. It is a biguanide with an entirely different mechanism. It may raise GLP-1 levels slightly as a downstream effect, but that does not make it a member of this class. I prescribe both, often together, in women with PMOS.

Foundayo (orforglipron), approved April 1, 2026, is worth calling out separately. It is the first small-molecule, non-peptide GLP-1 agonist: an oral pill with no food or water restrictions, taken any time of day.³ That solves the compliance problem that has limited Rybelsus, which must be taken fasting with minimal water and a 30-minute wait before eating.

Which one produces the most weight loss

Tirzepatide leads on efficacy. The oral option, Foundayo, does not match the injectables on magnitude, and patients should know that before choosing convenience over potency. That said, the best drug is the one a patient will take consistently, can afford, and can tolerate. I have had patients do better on semaglutide than tirzepatide because the side effects were more manageable for them, despite the trial data favoring tirzepatide.

Side effects

Lean mass loss is my main concern

In the DXA body-composition substudies, lean tissue accounted for roughly 38–40 percent of total weight lost on semaglutide in STEP 1 and about 25 percent on tirzepatide in SURMOUNT-1.⁹ Context matters: a conventional caloric deficit without medication produces a similar ratio, near 25 percent. These drugs do not have a unique muscle-wasting mechanism. The deficit is the mechanism, and the drug is what creates the deficit.

What that means practically is that the ratio is modifiable. Resistance training with adequate protein shifts it substantially toward fat loss.⁹ I treat strength training as part of the prescription, not an optional add-on.

Weight returns when the drug stops

In the STEP 1 extension, patients regained roughly two-thirds of the weight they had lost within a year of stopping semaglutide.¹⁰ The appetite suppression disappears when the drug does. This does not mean every patient needs lifelong therapy, but it does mean every patient needs a plan for what comes after.

Is it safe?

Safe compared to what, for whom, and for how long. Against the consequences of untreated obesity — type 2 diabetes, cardiovascular disease, sleep apnea, fatty liver, several cancers, joint destruction — the risk-benefit calculus favors treatment in patients who meet clinical criteria. SELECT showed a 20 percent reduction in cardiovascular events.² The FLOW trial demonstrated kidney protection in patients with type 2 diabetes and chronic kidney disease.¹¹

Two regulatory updates from the past year are worth knowing. The FDA removed the suicidal-ideation warning from GLP-1 labeling after review found no causal link. The European Medicines Agency added NAION as a very rare adverse effect of semaglutide.⁸

Five-plus years of semaglutide data and a shorter record for tirzepatide are reassuring for the populations studied. Lifetime data do not exist. I review the decision to continue at every visit, and I do not support obtaining these drugs without a physician relationship, baseline labs, and ongoing monitoring.

PMOS, fertility, and pregnancy

In May 2026, an international consensus published in The Lancet renamed polycystic ovary syndrome to polyendocrine metabolic ovarian syndrome, or PMOS. The old name implied ovarian cysts that are not actually cysts, and it obscured what is fundamentally a multisystem endocrine and metabolic disorder affecting roughly one in eight women.¹² The condition is the same. The name now describes it accurately.

PMOS is, at its core, a disorder of insulin resistance, which is precisely what GLP-1 agonists address. They are not FDA-approved for this indication, but the evidence is accumulating. An early proof-of-concept analysis from the ongoing RESTORE trial at the University of Colorado Anschutz, published in Fertility and Sterility in June 2026, found improved reproductive measures in participants aged 12 to 35 who achieved at least 10 percent weight loss on injectable semaglutide. The investigators reported that reproductive improvements appeared earlier than expected, which is why they published preliminary findings while the trial continues.¹³

I use GLP-1 agonists in PMOS patients frequently, often alongside metformin. Weight loss and insulin sensitization can restore ovulation, lower androgens, and change a patient's long-term metabolic trajectory.

The warning that comes with that benefit

The same improvements that help PMOS can produce an unintended pregnancy. A woman who has been anovulatory for years may resume ovulation within weeks of starting treatment, often before she notices any change in her cycle. If pregnancy is not desired, reliable contraception starts on day one of therapy, not later.

There is a specific interaction that gets too little attention: tirzepatide can reduce absorption of oral contraceptives because it slows gastric emptying. A patient starting Mounjaro or Zepbound on a combined oral pill should switch to a non-oral method — IUD, implant, or ring — or use backup protection through the titration period.

These drugs must be stopped before attempting pregnancy. Given semaglutide's week-long half-life, I use a washout of at least two months, and similar for tirzepatide. Liraglutide clears faster, which is one reason I sometimes prefer it in patients planning conception within the year. Data on inadvertent early-pregnancy exposure have not shown a clear increase in major birth defects, but the data are too limited to call these drugs safe in pregnancy.

The 2026 breast cancer signal

At the 2026 ASCO Annual Meeting, Elizabeth McDonald and colleagues at Penn Medicine presented a retrospective analysis of 111,646 women aged 45 to 80 with a BMI of 25 or higher who underwent breast imaging. Among 15,264 GLP-1 users, breast cancer was diagnosed in 1.62 percent, versus 2.31 percent among 96,382 non-users. In the matched analysis controlling for age, race, breast density, BMI, and diabetes status, GLP-1 use was associated with roughly 30 percent lower odds of a breast cancer diagnosis (OR 0.75, 95% CI 0.63–0.88).¹⁴

This is observational data. It does not establish causation, and the investigators said so plainly. But obesity is one of the few modifiable risk factors for postmenopausal breast cancer, and these drugs act on insulin signaling, inflammation, and metabolic regulation — all plausible pathways. A prospective multisite trial is being organized to test whether GLP-1 therapy can lower breast cancer incidence in high-risk women.¹⁴ I am watching that closely.

Raising GLP-1 without a prescription

Patients ask about this constantly, and the honest answer requires a caveat first: endogenous GLP-1 survives about two minutes before DPP-4 degrades it, while a pharmaceutical agonist maintains elevated levels for days.¹ The magnitudes are not comparable. Dietary strategies support metabolic health. They do not replicate what these drugs do, and any product marketed as a "natural Ozempic" is overselling.

What does have a reasonable evidence base: protein at meals stimulates L-cell GLP-1 release and suppresses ghrelin. Fermentable fiber is fermented by gut bacteria into short-chain fatty acids, which in turn stimulate GLP-1 secretion. Both aerobic and resistance exercise improve GLP-1 sensitivity. Chronic sleep deprivation impairs GLP-1 signaling and worsens insulin resistance. None of this is exotic, and none of it is a substitute for pharmacotherapy in a patient who needs it.

A word on patches

Products sold over the counter as "GLP-1 patches" are not GLP-1 receptor agonists. They are dietary supplements containing herbal or fiber ingredients, and no randomized trial has shown that any of them produces clinically meaningful weight loss. Transdermal microneedle delivery of actual GLP-1 peptides is under development, but nothing of the kind has FDA approval. If it is available without a prescription, it is not delivering a prescription drug.

Microdosing

Many patients use lower-than-labeled doses, often staying at the 0.25 mg semaglutide starting dose indefinitely. There is a logic to it. Starting doses are sub-therapeutic by design, existing to allow gastrointestinal adaptation, yet some patients get appetite reduction and modest weight loss even there.

The practice has not been studied by the FDA, and it likely does not deliver the cardiovascular and renal benefits shown in trials that used specific higher doses.^2,11 But if a patient cannot tolerate escalation and is benefiting at a low dose, I would rather keep her on a tolerable dose than lose her from treatment altogether. That is a conversation to have with a prescriber, not a decision to make alone.

Cost and coverage

Cost remains the largest barrier. Wegovy lists around $1,300 to $1,400 monthly without insurance; Zepbound around $1,060, with an Eli Lilly self-pay program at $299 per month for the KwikPen. Foundayo self-pay starts at $149 monthly for the lowest dose, and eligible commercially insured patients may pay as little as $25.³ Generic liraglutide, approved in late 2024, has begun to pull that older drug's price down. No generic semaglutide or tirzepatide exists.

Medicare

This changed on July 1, 2026, when the Medicare GLP-1 Bridge Program took effect. Eligible Part D beneficiaries can access Wegovy, Zepbound (KwikPen), or Foundayo for weight loss at a fixed $50 monthly copay. The program runs through December 31, 2027.¹⁵

Patients already on a GLP-1 before July 2026 qualify if they met the BMI threshold when therapy began, even if their current BMI has since fallen below it.¹⁵

What is coming

The drugs available now are probably not the most effective ones we will see. Retatrutide, a triple agonist targeting GLP-1, GIP, and glucagon receptors, produced up to 24.2 percent weight loss at 48 weeks in phase 2 and is in phase 3 trials.¹⁶ CagriSema, combining semaglutide with an amylin analogue, is under FDA review. Survodutide, a GLP-1/glucagon dual agonist, is in phase 3.

The pattern is more receptors engaged, more weight lost. The constraint is tolerability: greater potency brings more gastrointestinal burden during titration, which is why the engineering of dose escalation now matters as much as efficacy.

What I tell patients

These are tools, not shortcuts. They work best with a protein-forward, fiber-rich diet, resistance training, adequate sleep, and stress management. The patients who do best long-term use the period of appetite suppression to build habits that outlast the prescription.

Titrate slowly. Rushing to the maximum dose is the most common reason patients end up miserable and quit. More time at each step means better tolerance.

Prioritize protein deliberately. When appetite is suppressed, patients eat less of everything, protein included. Protein intake has to become intentional, not incidental. This is what protects lean mass.

Train against resistance. Without it, too much of what is lost is muscle, and muscle loss slows metabolism, weakens bone, and makes regain more likely.

If you have PMOS and are not using reliable contraception, start now. Ovulation can return before you notice any change in your cycle.

Get baseline labs and repeat them. This is standard care, not optional care.

These drugs have changed outcomes for patients I treated for years without adequate tools. They work best when prescribed thoughtfully, monitored carefully, and used inside a broader plan. If you are wondering whether one is right for you, have that conversation with your physician — not a website, and not a telehealth service that will write a prescription without labs.

References

1. Holst JJ. The physiology of glucagon-like peptide 1. Physiol Rev. 2007;87(4):1409–1439. doi:10.1152/physrev.00034.2006. PMID 17928588
2. Lincoff AM, Brown-Frandsen K, Colhoun HM, et al; SELECT Trial Investigators. Semaglutide and cardiovascular outcomes in obesity without diabetes. N Engl J Med. 2023;389(24):2221–2232. doi:10.1056/NEJMoa2307563. PMID 37952131
3. US Food and Drug Administration. FOUNDAYO (orforglipron) tablets — full prescribing information. Approved April 1, 2026. accessdata.fda.gov. See also Eli Lilly and Company. FDA approves Lilly's Foundayo (orforglipron). April 1, 2026. ATTAIN-1 efficacy and pricing data as reported therein.
4. Jastreboff AM, Aronne LJ, Ahmad NN, et al; SURMOUNT-1 Investigators. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205–216. doi:10.1056/NEJMoa2206038. PMID 35658024
5. Wharton S, Freitas P, Hjelmesæth J, et al; STEP UP Trial Group. Once-weekly semaglutide 7·2 mg in adults with obesity (STEP UP): a randomised, controlled, phase 3b trial. Lancet Diabetes Endocrinol. 2025. doi:10.1016/S2213-8587(25)00226-8
6. Wilding JPH, Batterham RL, Calanna S, et al; STEP 1 Study Group. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989–1002. doi:10.1056/NEJMoa2032183. PMID 33567185
7. Pi-Sunyer X, Astrup A, Fujioka K, et al; SCALE Obesity and Prediabetes NN8022-1839 Study Group. A randomized, controlled trial of 3.0 mg of liraglutide in weight management. N Engl J Med. 2015;373(1):11–22. doi:10.1056/NEJMoa1411892
8. European Medicines Agency, 2025: non-arteritic anterior ischaemic optic neuropathy (NAION) added to semaglutide product information as a very rare adverse effect. Separately, the US FDA concluded its review of a possible suicidal-ideation signal with GLP-1 receptor agonists and found no causal association. Consult current product labeling for both.
9. Dual-energy X-ray absorptiometry (DXA) body-composition substudies of the STEP 1 and SURMOUNT-1 trials. Lean soft tissue comprised approximately 26–40% of total weight lost across recent GLP-1 and GLP-1/GIP trials; see review and accompanying case series documenting lean-mass preservation with resistance training and adequate protein at PMC12536186.
10. Wilding JPH, Batterham RL, Davies M, et al; STEP 1 Study Group. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes Obes Metab. 2022;24(8):1553–1564. doi:10.1111/dom.14725
11. Perkovic V, Tuttle KR, Rossing P, et al; FLOW Trial Committees and Investigators. Effects of semaglutide on chronic kidney disease in patients with type 2 diabetes (FLOW). N Engl J Med. 2024. PMID 38785209
12. Teede HJ, et al. Polyendocrine metabolic ovarian syndrome, the new name for polycystic ovary syndrome: a multistep global consensus process. The Lancet. May 12, 2026. doi:10.1016/S0140-6736(26)00717-8. Developed through a consortium of 56 patient and professional organizations; endorsed by the Endocrine Society and the American Society for Reproductive Medicine.
13. Cree MG, Garcia-Reyes Y, Shapiro A, et al. Weight loss associated with semaglutide use is linked to improved reproductive measures in PMOS: a proof-of-concept analysis. Fertil Steril. 2026. University of Colorado Anschutz Medical Campus, RESTORE trial.
14. McDonald ES, Gillis L, Gabriel P, et al. GLP-1 agonists are associated with a significant reduction in breast cancer incidence in women. JCO Oncol Pract. Published online June 2, 2026. doi:10.1200/OP-26-00485. Presented at the 2026 ASCO Annual Meeting, Abstract 10506.
15. Centers for Medicare & Medicaid Services. Medicare GLP-1 Bridge: coverage criteria and beneficiary FAQ. Updated June 2026. cms.gov
16. Jastreboff AM, Kaplan LM, Frías JP, et al. Triple-hormone-receptor agonist retatrutide for obesity — a phase 2 trial. N Engl J Med. 2023;389(6):514–526. doi:10.1056/NEJMoa2301972. PMID 37366315

This article is educational and does not constitute medical advice or establish a physician-patient relationship. GLP-1 receptor agonists are prescription medications requiring medical supervision. Individual results vary. Consult your own physician before starting, changing, or discontinuing any medication.