Bioequivalence means two versions of a medicine deliver the active ingredient at a comparable rate and in a comparable amount. The active ingredient is the part responsible for the medicine's effects. A generic, a version made to match an existing medicine, uses this comparison to establish comparable performance. It doesn't mean every ingredient, or every person's response, is identical.
What is bioequivalence in FDA's definition?
Under 21 CFR 320.23, the comparison concerns how quickly and how much of the active medicine is absorbed. The products are studied at the same amount of active medicine under similar conditions. Some differences in absorption speed can qualify if they are intentional, described in labeling and too small to matter for treatment.
As of September 30, 2026, the day this article was written, that eCFR page is marked “up to date as of 9/29/2026.” Section 320.24 describes the evidence FDA can require, including blood measurements and laboratory methods. There isn't one test that fits every medicine.
Why the term exists
The comparison lets a generic applicant rely on the brand's established treatment evidence without repeating every large trial. An ANDA, or abbreviated new drug application, is the filing for that route. FDA still examines the finished product's required sameness, manufacturing and performance (FDA's ANDA overview).
Liraglutide shows that peptide generics are possible. FDA's 2024 first-generics list, marked “Content current as of: 10/23/2025,” records Hikma's first generic referencing Victoza on December 23, 2024.
Separately, a 36-volunteer liraglutide study by Liu and colleagues, Frontiers in Pharmacology, 2023, compared two formulations, or preparations of the medicine, in the same people at different visits. It illustrates the comparison; it was not a study of Hikma's product.
As of September 30, 2026, the day this article was written, Gopalakrishnan and colleagues' July 6 paper in Diabetes, Obesity and Metabolism adds a clinical comparison of synthetic semaglutide, made chemically, against Wegovy. It compared weight change over 24 weeks in 267 adults in India. Treatment outcomes answer a different question from blood levels; neither comparison establishes equivalence for pharmacy-compounded semaglutide.
How the 80–125% rule works
Blood samples give two useful measurements:
- AUC, or area under the curve: total exposure to the medicine in the blood over time.
- Cmax: the highest level of the medicine measured in the blood.
AUC reflects how much medicine reaches the blood. Cmax helps assess how quickly it arrives (FDA's explanation of the measurements).
Researchers compare the study averages for the test medicine and the reference product, the medicine it is being matched against. A ratio expresses the test medicine’s average as a percentage of the reference’s. A confidence interval is the range that expresses uncertainty around that comparison.
As of September 30, 2026, the day this article was written, FDA's current statistical guidance is dated “May 2026.” For the usual blood-level comparison, the entire 90% confidence interval for each average ratio must fit between 80% and 125%.
Imagine a study reported these intervals:
| Illustrative interval | Meets the usual limit? |
|---|---|
| 95%–105% | Yes: the whole interval fits. |
| 78%–103% | No: one end falls outside it. |
This is not permission to put 80% of the labeled dose into a medicine. The limits concern study comparisons, not ingredient content. Some medicines need different statistical approaches.
Semaglutide and tirzepatide show the distinction
As of September 30, 2026, the day this article was written, Health Canada's releases document generic Ozempic decisions for Dr. Reddy's on April 28 and Apotex on May 1, 2026. Those are Canadian product decisions. Our guide to semaglutide from Canada explains availability and the separate U.S. import rules.
As of September 30, 2026, the day this article was written, Sandoz's June 29, 2026 release documents FDA acceptance of two tirzepatide ANDAs, referencing Mounjaro and Zepbound. Acceptance means review can begin; it doesn't mean the comparisons passed. The generic tirzepatide guide follows that application story.
Why peptide generics need more comparisons
Peptides are short chains of amino acids, the building blocks of proteins. Matching one involves more than measuring blood levels. Developers also compare the chain's structure, how it behaves and impurities, the unwanted substances left from making or storing it.
FDA's May 2021 guidance addressed synthetic peptides referencing products made using engineered living cells. That document is now historical.
As of September 30, 2026, the day this article was written, FDA's July 28 announcement reports 17 revised draft product-specific guidances and withdrawal of the 2021 document. Its stamp reads “Content current as of: 07/28/2026.” The drafts include semaglutide and tirzepatide and update recommendations on structure, activity, impurities and possible reactions from the body’s defenses. They are draft recommendations, rather than decisions on an individual application.
A study in people isn't mandatory for every generic. The tirzepatide draft, marked “Revised Jul 2026,” describes requesting a waiver, permission to omit a study in people, when formulation conditions are met. A waiver changes the required evidence; it doesn't erase the product comparison.
Compounded medicines are a separate route
A compounded preparation is not a generic: a true generic must complete FDA's review and meet its standards for sameness and equivalence. Compounded drugs do not go through that generic bioequivalence testing and review. A pharmacy quality test doesn't establish that a preparation matches a brand's performance.
Through Promise, semaglutide is dispensed as a compounded medication, which is different from an FDA-approved product: the formulation offered here is not FDA-approved. Tirzepatide also comes through a compounded prescription. FDA explains that compounded drugs are not reviewed by the agency for safety, effectiveness or quality before marketing.
A licensed provider may still prescribe a compounded formulation; that decision is between you and your doctor.
Common mistakes and related terms
“Same ingredient” doesn't settle the finished-product comparison. Ingredient identity, formulation and evidence of equivalent performance are separate pieces.
Bioequivalence doesn't promise an identical experience. It supports the product comparison; individual response and side effects can still differ.
A filing isn't permission to market. FDA tentative approval describes an application that has cleared scientific review but still faces a legal barrier. Our clinical-trial phases guide explains the different questions asked when a medicine is first developed.
Bioavailability means how quickly and how much medicine becomes available where it acts. Bioequivalence compares products. Pharmaceutical equivalence means matching required features such as the active ingredient, strength and dosage form, the physical form of the medicine. Those terms describe different checks.
At Promise, a licensed provider reviews every request, and not everyone qualifies. The exact preparation and the person's medical history remain part of that review.
