Orforglipron vs Tirzepatide: Oral Pill vs Weekly Injection

Orforglipron vs Tirzepatide at a Glance

Orforglipron and tirzepatide come from the same company but are different kinds of molecule. Orforglipron is a “small-molecule, nonpeptide oral” GLP-1 receptor agonist, discovered by Chugai Pharmaceutical and licensed to Lilly in 2018.^[3][9] Tirzepatide is a single peptide that activates both the GIP and GLP-1 receptors.^[10][11]

The molecular weights are taken from each FDA label, and the approval dates from FDA records.^{[5][6][7][12]} The weight figures in the last row come from two separate trials, both on the treatment-regimen estimand, and are not a head-to-head result.^[3][4] For orforglipron on its own, see the orforglipron research profile; for tirzepatide against Lilly’s triple agonist, see retatrutide vs tirzepatide.

Is There a Head-to-Head Trial?

No. On October 12, 2026, a ClinicalTrials.gov search for studies that list both orforglipron and tirzepatide as interventions returned two records, and neither compares how well the two drugs work.^[1] One is ATTAIN-MAINTAIN, which tested orforglipron against placebo in people previously treated with tirzepatide or semaglutide.^[13] The other is a small University of Florida Phase 2 study with a single treatment group (about 20 people planned), in which each participant receives one GLP-1 drug from a list that includes both.^[1] Lilly’s development pipeline, with data as of August 5, 2026, lists no program that compares the two.^[2]

Every efficacy comparison on this page therefore sets results from separate trials side by side. Trials differ in population, years, background diet advice and statistical handling, so a gap between two trials is not proof that one drug beats the other.

Which Is More Effective? The Weight-Loss Data

The closest pairs are trials of the same length in similar people. ATTAIN-1 and SURMOUNT-1 each ran for 72 weeks in adults without diabetes. ATTAIN-2 and SURMOUNT-2 each ran for 72 weeks in adults with type 2 diabetes (T2D) and a body-mass index of 27 or more.^{[3][4][14][15]} The table compares the top arm of each trial: 36 mg of the investigational orforglipron formulation, which the Foundayo label presents as its top tablet strength, and 15 mg tirzepatide.^[12]

The two estimands answer different questions. Lilly defines the treatment-regimen estimand as the average effect “regardless of treatment discontinuation”, and the efficacy estimand as efficacy “prior to discontinuation of study drug”.^[11] ATTAIN-1 and SURMOUNT-1 both used the treatment-regimen estimand for their primary result; the efficacy-estimand figures come from Lilly’s releases.^{[3][4][11][16]} The placebo-adjusted rows for the trials without diabetes come from the intent-to-treat (ITT) analyses in the FDA labels, and those for the trials in T2D from the papers, on the treatment-regimen estimand.^{[5][12][14][15]}

The trials may also have differed in background advice, but the sources disagree. The ATTAIN-1 paper describes a “healthy diet and physical activity”, and Lilly says the trial used “a balanced, healthy diet rather than a reduced-calorie diet”, whereas SURMOUNT-1 used a reduced-calorie diet and increased physical activity. The Foundayo label, however, says patients in both ATTAIN trials received instruction on a reduced-calorie diet.^{[3][16][11][12]} Tirzepatide’s results were larger in each matched pair, but no trial has tested whether that gap holds in a direct comparison, and these data cannot show why it exists. For how the receptor targets differ, see GLP-1, GIP and glucagon mechanism of action.

The BMJ network meta-analysis pooled 262 randomized trials and compared each drug with lifestyle change alone at one year: tirzepatide −14.9% (95% CI −16.0 to −13.9) and orforglipron −9.9% (−12.4 to −7.5), with moderate to high certainty evidence.^[8] A network meta-analysis is still an indirect comparison.

Blood sugar is less clear. No trial compares the two drugs on HbA1c. Orforglipron’s type 2 diabetes program includes ACHIEVE-3, an open-label 52-week trial in which it lowered HbA1c more than oral semaglutide; tirzepatide was not a comparator.^[17] For that oral head-to-head, see Foundayo vs the Wegovy pill.

Foundayo vs Zepbound and Mounjaro: The Brand Names

Foundayo is the brand name of orforglipron. Its only US indication is chronic weight management in adults with obesity, or overweight with at least one weight-related condition, alongside a reduced-calorie diet and increased physical activity.^[12] Lilly submitted orforglipron to FDA for type 2 diabetes in the second quarter of 2026, and that use is still under review.^[18][2]

Tirzepatide has two US brand names. Zepbound is approved for chronic weight management and for moderate to severe obstructive sleep apnea in adults with obesity.^[5] Mounjaro is the type 2 diabetes brand: it is approved for blood-sugar control in adults and in children aged 10 and over, and, since August 27, 2026, to reduce the risk of major adverse cardiovascular events in adults with type 2 diabetes at high risk.^[19][20] Mounjaro has no US weight-management indication, although Lilly says tirzepatide is approved as Mounjaro “in some countries outside the U.S.” for obesity or overweight as well.^[9]

Foundayo vs Zepbound is therefore a comparison of two US weight-management medicines, while Foundayo vs Mounjaro, in the US, compares a weight-management pill with a diabetes injection. Both labels advise against combining their drug with another GLP-1 receptor agonist, and Zepbound’s label also names other tirzepatide-containing products.^[5][12] For the cardiovascular data behind Mounjaro’s newest indication, see tirzepatide vs semaglutide cardiovascular outcomes.

Is Orforglipron a Peptide? Small Molecule vs Peptide

No. Orforglipron is a small-molecule, nonpeptide drug.^[3] A 2020 structural study of the compound, then coded LY3502970, described it as a partial agonist at the GLP-1 receptor, biased toward G-protein signaling over beta-arrestin recruitment, and noted that the GLP-1 receptor agonists approved at the time were all peptide based. The authors also reported a pharmacokinetic profile favorable for oral use.^[21] The Foundayo label gives a molecular weight of 902.0 g/mol for orforglipron calcium and describes it as insoluble in water.^[12]

Tirzepatide is a peptide. Lilly’s discovery paper describes it as “a 39 amino acid linear peptide conjugated to a C20 fatty diacid moiety”, and its label says it is based on the GIP sequence, with a molecular weight of 4,813.53 Da.^[5][10] US regulations define a protein as an amino-acid chain “greater than 40 amino acids in size”, so at 39 residues tirzepatide sits on the peptide side of the line, and both of its brands were approved as new drug applications.^[6][20][22] Lilly’s pipeline lists orforglipron as a small molecule and tirzepatide as a large molecule, a category Lilly says covers “proteins, peptides or antibodies”.^[2]

Orforglipron weighs about one-fifth as much as tirzepatide. The rodent biology differs as well: the Foundayo label says orforglipron “is not pharmacologically active in rats or mice and did not produce tumors in rodents”, whereas tirzepatide caused thyroid C-cell tumors in rats. Both labels carry a boxed warning for thyroid C-cell tumors.^[5][12] For how the 40-amino-acid rule applies to another Lilly incretin, see is retatrutide a peptide or a biologic?, and for the basics, what are peptides?

Orforglipron Pill vs Tirzepatide Injection

The most visible difference is the format. Foundayo is a film-coated tablet taken once a day, while Zepbound and Mounjaro are once-weekly injections under the skin.^[5][19][12] FDA’s acting drug-center director described Foundayo as “a GLP-1 receptor partial agonist pill”.^[7]

Format also shapes the side-effect lists. Injection-site reactions occur only with the injectable: 8% against 2% with placebo at Zepbound’s top strength in its label’s pooled trials.^[5] This page does not describe how either medicine is taken. For the oral class as a whole, see oral GLP-1 drugs for weight loss in 2026.

Side Effects Compared

Both drugs mainly cause gastrointestinal side effects. The table sets the label rates for the top strength of each against placebo, from each label’s pooled placebo-controlled weight-management trials.^[5][12] Both labels warn that adverse reaction rates “cannot be directly compared to rates in the clinical trials of another drug”.^[5][12]

The BMJ network meta-analysis placed orforglipron among the drugs with the highest discontinuation for adverse events (risk ratios of 1.9 to 4.2 for that group), found gastrointestinal events increased with both orforglipron and tirzepatide, and estimated a fatigue risk ratio of 3.4 for orforglipron.^[8] Beyond the boxed warning, both labels list warnings for pancreatitis, severe gastrointestinal reactions, kidney injury from fluid loss, low blood sugar, gallbladder disease, diabetic retinopathy complications in people with type 2 diabetes and aspiration under anesthesia.^[5][12] For the injectable class, see Wegovy vs Ozempic vs Mounjaro side effects.

Orforglipron After Tirzepatide: The ATTAIN-MAINTAIN Trial

ATTAIN-MAINTAIN tested orforglipron against placebo in people previously treated with tirzepatide or semaglutide, and it is a maintenance study, not a head-to-head comparison.^[13] It enrolled people who had completed SURMOUNT-5, an open-label trial of tirzepatide against semaglutide, and its primary result covers those who had reached a weight plateau there, defined as less than 5% weight change between weeks 60 and 72.^[13][9][23] The 376 participants, all in the US, were randomized 3:2 to once-daily orforglipron or placebo for 52 weeks, double-blind: 205 had been on tirzepatide and 171 on semaglutide.^[9][13]

The percentages are shares of prior weight loss kept at week 52, on the treatment-regimen estimand reported in Nature Medicine, published online on May 13, 2026. The primary result covers participants who had reached a plateau, with 95% confidence intervals for the differences; the “All” rows cover everyone randomized.^[13] For the primary endpoint, Lilly’s release gives 78.0% after Zepbound and 82.4% after Wegovy without naming the estimand; both are higher than the paper’s treatment-regimen figures.^[9][13] The kilogram figures are Lilly’s, from the efficacy-estimand data set: observed weights at the switch and modelled weights at week 52.^[9] The paper lists as limitations “the absence of a comparator arm involving continued use of injectable obesity-management medications” and the trial’s one-year length.^[13] It shows that orforglipron held weight better than placebo after tirzepatide; it does not show how orforglipron compares with staying on tirzepatide.

A separate Lilly trial with no orforglipron, SURMOUNT-MAINTAIN, found that people who continued Zepbound unchanged after 60 weeks kept all of their prior weight loss on average, while those moved to its 5 mg arm kept all but 5.6 kg.^[9] Comparing the two maintenance trials is again cross-trial. This page gives no switching or transition guidance. For regain after treatment stops, see GLP-1 discontinuation and weight regain data.

US Self-Pay Cost: Foundayo vs Zepbound

As of October 12, 2026, Lilly’s own US pharmacy service lists self-pay prices for both brands. Foundayo starts at $149 a month and reaches $299 a month for the higher strengths. The two highest strengths cost $299 only when each refill is bought within 45 days, and two of the lower prices are temporary cuts that run through December 31, 2026. Lilly’s Foundayo month is 30 days.^[24] Zepbound, as a KwikPen or as vials, starts at $299 a month and reaches $449 a month under Lilly’s refill program. If a refill is late, the higher strengths cost $499 to $699. Lilly’s Zepbound month is 28 days.^[25]

Both pages say commercially insured patients whose plans cover the medicine may pay as little as $25 a month under Lilly’s savings programs (for Zepbound, with the pen that LillyDirect offers only to insured patients), subject to terms.^[24][25] These are US prices only, and they change often. For the full Foundayo price table, see our Foundayo approval page.

Regulatory Status

• Foundayo (orforglipron). FDA approved it on April 1, 2026 for chronic weight management, the first new molecular entity approved under the Commissioner’s National Priority Voucher pilot, 50 days after filing.^[7] Its type 2 diabetes application, submitted to FDA in the second quarter of 2026, is under review.^[18][2] Foundayo was approved in the UAE in early April 2026; our Foundayo approval page has the details.
• Zepbound (tirzepatide). Approved for chronic weight management on November 8, 2023, and for obstructive sleep apnea in adults with obesity on December 20, 2024.^[6]
• Mounjaro (tirzepatide). Approved for type 2 diabetes; the cardiovascular risk-reduction indication, based on the SURPASS-CVOT trial, was added on August 27, 2026.^[19][20]

For the wider picture, see Is orforglipron approved?, the 2026 obesity drug approval tracker and retatrutide vs Foundayo.

What This Page Does Not Cover

This page summarizes published trials, FDA labels and records, a registry search and Lilly’s own releases and price pages. It gives no dosing, switching, prescribing or administration guidance and makes no therapeutic, human-use or veterinary claim. Cross-trial figures do not predict how either medicine would perform in a direct comparison.