Compounded Semaglutide vs Wegovy: Bioequivalence Evidence Review

The honest answer: Compounded semaglutide is not FDA-tested for bioequivalence to Wegovy. No such study has ever been required, run, or published. The 2022 to early-2025 FDA shortage listing temporarily permitted §503A and §503B compounding; that window closed in February 2025, and the agency is now actively issuing warning letters.^[1]

At a glance

• Zero bioequivalence trials comparing any compounded semaglutide preparation to FDA-approved Wegovy exist in the public literature.^[2]
• The FDA-approved Wegovy formulation is the semaglutide base peptide (molecular weight 4113.58 g/mol) in a sterile aqueous solution. Many compounded products use salt forms (semaglutide sodium, semaglutide acetate) that have never appeared in any FDA approval.^[3]
• The §503A and §503B compounding carveouts never required bioequivalence testing. They were designed for patient-specific preparations, not for parallel mass markets.^[1]
• The FDA removed semaglutide injection from its drug-shortage list on February 21, 2025, ending the §506E legal hook that had permitted scaled compounding.^[4]
• The FDA's GLP-1 safety page warns that “patients and health care professionals should be aware that FDA does not review compounded versions of these drugs for safety, effectiveness, or quality.”^[5]
• In 2025 to 2026, the FDA issued warning letters to multiple compounders selling semaglutide online, citing unapproved-new-drug and misbranding violations.^[6][7][8]

What “bioequivalence” actually means at FDA

The FDA's definition of bioequivalence is narrow and operational. Two drug products are bioequivalent when “the rate and extent to which the active ingredient or active moiety becomes available at the site of drug action” shows no significant difference at the same molar dose under similar conditions. In practice that means healthy-volunteer pharmacokinetic studies measuring the plasma area under the curve (AUC) and peak concentration (Cmax), with the generic product's 90% confidence interval required to fall within 80–125% of the reference product on both metrics.^[1]

Bioequivalence is the regulatory mechanism by which generic drugs get approved as substitutable for brand-name originators through the Abbreviated New Drug Application (ANDA) pathway. Compounded products are not generic drugs, do not file ANDAs, and by definition have not undergone bioequivalence testing. This is not a loophole; it is the explicit structure of the compounding statute.^[1]

Anyone marketing a compounded GLP-1 as “bioequivalent to Wegovy” is using the word colloquially (“basically the same”) rather than in the regulatory sense, and the distinction matters because no compounded product on the U.S. market carries the data that would support the regulatory claim.

Wegovy's FDA-approved formulation (DailyMed verbatim)

The current Wegovy prescribing information on DailyMed describes the active ingredient verbatim as:

“WEGOVY contains semaglutide, a human GLP-1 receptor agonist (or GLP-1 analog). The peptide backbone is produced by yeast fermentation. The main protraction mechanism of semaglutide is albumin binding, facilitated by modification of position 26 lysine with a hydrophilic spacer and a C18 fatty di-acid. … The molecular formula is C₁₈₇H₂₉₁N₄₅O₅₉ and the molecular weight is 4113.58 g/mol.”^[3]

The §3 Dosage Forms and Strengths section lists single-dose prefilled pens and prefilled syringes in escalation strengths of 0.25, 0.5, 1, 1.7, and 2.4 mg, plus a 7.2 mg WEGOVY HD pen and tablet strengths of 1.5, 4, and 9 mg. Every strength is characterized as a “clear, colorless solution” with the active ingredient identified as semaglutide (no salt qualifier).^[3]

This matters because the molecular weight (4113.58 g/mol) is the base-form weight. Semaglutide sodium and semaglutide acetate have different molecular weights and have not been evaluated in any pivotal trial submitted to the FDA. The STEP-1 efficacy data that underpinned Wegovy's 2021 weight-loss approval used the base form exclusively.^[9]

Why the §503A shortage window enabled the compounded market

Under §503A of the Federal Food, Drug, and Cosmetic Act, a traditional state-licensed compounding pharmacy cannot compound a drug that is “essentially a copy” of a commercially available FDA-approved product. That rule exists to stop compounders from undercutting brand manufacturers on patented medications. The statutory exception is §506E (codified at 21 U.S.C. §356e), which directs the FDA to maintain a public drug-shortage list. When a drug is on that list, the “essentially a copy” prohibition is temporarily lifted.^[1]

Semaglutide injection was added to the FDA drug-shortage list in March 2022 as Novo Nordisk struggled to keep up with Ozempic and Wegovy demand. That listing — which persisted until February 2025 — was the legal hook that made it possible for §503A pharmacies and §503B outsourcing facilities, plus the telehealth platforms that contract with them, to compound and dispense semaglutide at scale. The §506E carveout was clearly intended to keep hospital infusions and oncology drugs flowing during supply disruptions, not to stand up a parallel direct-to-consumer retail market for weight-loss injections, but the statute does not distinguish.^[4]

On February 21, 2025, the FDA officially resolved the semaglutide-injection shortage and posted the revised status to its public shortages database. The compounding carveout under §506E technically closed for semaglutide on that date, with a brief wind-down window for §503A pharmacies (through approximately April 2025) and §503B outsourcing facilities (through approximately May 2025) before enforcement priority shifted.^[4]

What the FDA's GLP-1 safety page warns about compounded products

The FDA's dedicated patient-and-provider page on FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss is unambiguous. It states:

“Patients and health care professionals should be aware that FDA does not review compounded versions of these drugs for safety, effectiveness, or quality.”^[5]

The same page specifies that newer GLP-1s including retatrutide and cagrilintide “cannot be used in compounding under federal law” because they are not yet approved at all, separating those investigational molecules from the semaglutide-specific shortage carveout that briefly applied.^[5]

The page also flags specific recurring failure modes the agency has logged in adverse-event reports tied to compounded GLP-1s: dosing errors (semaglutide is dosed in fractions of a milligram, and microgram/milligram confusion produces tenfold overdoses); use of salt forms not used in the FDA-approved products; and products from sources without documented quality controls.^[5]

FDA enforcement: warning letters to compounders 2025 to 2026

Since the shortage resolution, the FDA Center for Drug Evaluation and Research (CDER) has issued multiple warning letters targeting online sellers of unapproved semaglutide. Two representative letters from September 9, 2025 cite GLP-1 Solution^[6] and ASN-LABS^[7] for selling unapproved drug products over the internet. Two March 31, 2026 letters expanded enforcement to Prime Sciences^[8] and Mile High Compounds LLC^[10], both cited under the same “Unapproved New Drugs Sold Over the Internet” statutory framing covering both semaglutide and tirzepatide.

The violation pattern across these letters is consistent: marketing as a substitute for FDA-approved Wegovy or Ozempic without an approved new drug application, misbranding under the Federal Food, Drug, and Cosmetic Act, and in several cases failure to register as a drug manufacturer at all. The ongoing live dataset of every FDA warning letter we have identified against GLP-1 compounders is at FDA warning letters to compounded GLP-1 telehealth providers.

Salt forms, potency variability, and sterility risk

The active-ingredient distinction is not academic. A 2025 analysis of the direct-to-consumer compounded GLP-1 market in Colorado documented that providers routinely market compounded preparations to patients without disclosing whether the API is the base peptide or a salt form, and without disclosing the source pharmacy.^[2]

Even when the molecule is the base peptide, compounded preparations are not required to meet the same potency-band and stability requirements as FDA-approved products. United States Pharmacopeia (USP) chapters governing sterile compounding (notably USP <797>) require sterility and endotoxin testing for finished sterile preparations, but §503A pharmacies are not required to run bioavailability studies, head-to-head clinical comparisons, or long-term stability programs comparable to a brand-name manufacturer. The §503B outsourcing-facility framework layers cGMP requirements on top of USP, narrowing but not eliminating the gap.^[5]

For context on what FDA-approved semaglutide actually delivers in a controlled trial, the STEP-1 pivotal study (Wilding et al., 2021, NEJM) randomized 1,961 adults with obesity to once-weekly semaglutide 2.4 mg versus placebo and showed a mean placebo-adjusted body-weight change of -12.4 percentage points at week 68.^[9] That magnitude reflects the FDA-approved formulation, FDA-approved dosing, and FDA-required quality controls. None of those parameters automatically transfer to a compounded preparation.

If you're on compounded semaglutide today, what to do

For patients currently using a compounded preparation, the practical checklist is short:

1. Identify the source pharmacy in writing. The telehealth provider should name a specific 503A or 503B facility. “Our network of partner pharmacies” is not an answer.
2. Ask which salt form is used. Semaglutide base is the form in Wegovy. Sodium or acetate salts are the forms the FDA has flagged.
3. Request a certificate of analysis for the lot you receive, documenting identity, potency, and sterility.
4. Verify dosing in milligrams, not units or milliliters. The most common compounded-GLP-1 adverse event in FDA reports is microgram/milligram confusion producing tenfold overdoses.^[5]
5. Discuss transition to an FDA-approved product with a clinician. Novo Nordisk's direct-pay channels and FDA-approved alternative oral GLP-1 options may now be price-competitive with what compounded providers charge.

Practical takeaway

Compounded semaglutide is not FDA-bioequivalent to Wegovy, has never been required to be, and the statutory window that briefly legalized its mass-market distribution closed on February 21, 2025. The molecule may or may not be the same active ingredient depending on which salt form a particular pharmacy sourced. The product may or may not meet the potency it claims depending on which pharmacy compounded it. The agency is now actively enforcing against online sellers through warning letters and is unlikely to reopen the shortage carveout absent a renewed supply disruption.

For background on the operational details — what 503A and 503B pharmacies actually test, salt-form chemistry, and the PCAB accreditation framework — see Compounded semaglutide bioequivalence: what 503A pharmacies actually have to test. For the live FDA enforcement dataset, see FDA warning letters to compounded GLP-1 telehealth providers.