Reading a peptide label: FDA prescription labeling versus a research-use-only vial

An FDA-reviewed prescribing label and a research-use-only vial label differ in structure, content and regulatory status ^1,2.

The structure of an FDA prescribing label

Prescription labeling for drugs approved in the modern format is governed by 21 CFR 201.57, which specifies a Highlights section, a table of contents and the full prescribing information in a set order ¹. The current Wegovy label, for example, opens with a boxed warning headed "WARNING: RISK OF THYROID C-CELL TUMORS", which states that semaglutide causes dose- and duration-dependent thyroid C-cell tumours in rodents at clinically relevant exposures, that the human relevance has not been determined, and that the drug is contraindicated in people with a personal or family history of medullary thyroid carcinoma or MEN 2 ³. The regulation requires the box heading to contain the word "WARNING" in upper case, and requires the Highlights version to be followed by the verbatim sentence "See full prescribing information for complete boxed warning." ¹. The Zepbound label carries an equivalent boxed warning for tirzepatide, which it describes as observed in rats ⁴.

Indications and usage

Wegovy injection is indicated alongside a reduced-calorie diet and increased physical activity to reduce the risk of major adverse cardiovascular events in adults with established cardiovascular disease and obesity or overweight, and to reduce excess body weight and maintain weight reduction in specified populations ³. The Zepbound label lists weight reduction in adults with obesity or with overweight plus a weight-related comorbidity, and treatment of moderate to severe obstructive sleep apnoea in adults with obesity ⁴. An indication is a regulatory conclusion tied to specific trials and populations, not a general statement about what a molecule can do ¹.

Warnings, adverse reactions and the numbers behind them

The Warnings and Precautions section of the Wegovy label lists risks such as thyroid C-cell tumours and acute pancreatitis, with pancreatitis described as observed in patients treated with GLP-1 receptor agonists ³. Section 6.1 reports clinical-trial adverse reactions, and its Table 3 lists reactions occurring in at least 2% of Wegovy-treated adults and more often than with placebo: nausea in 44% versus 16%, diarrhoea in 30% versus 16%, vomiting in 24% versus 6% and constipation in 24% versus 11%, with dysesthesia at 2% versus 1% ³. The label cautions that rates observed in one programme cannot be directly compared with those from another and may not reflect rates in practice ³. It also carries the reporting statement required by regulation, directing readers to the manufacturer and to FDA's MedWatch ^1,3. The Zepbound label similarly reports a mean heart-rate increase of 1 to 3 beats per minute and dysesthesia in 0.2% to 0.4% of treated patients versus 0.1% with placebo ⁴.

Pharmacology, description and the package label

The Wegovy label states that semaglutide is a GLP-1 analogue whose peptide backbone is produced by yeast fermentation, gives its molecular weight as 4113.58 g/mol, and reports an elimination half-life of approximately one week ³. The Zepbound label gives a molecular weight of 4813.53 Da and a half-life of approximately five days ⁴. The carton labelling carries the NDC number, "Rx only", the route ("For subcutaneous use only") and an instruction to dispense the enclosed Medication Guide ^3,4.

What a research-use-only label is

The phrase "For Research Use Only. Not for use in diagnostic procedures." has a specific regulatory home: 21 CFR 809.10 allows it on in vitro diagnostic products that are in the laboratory research phase of development ². Nothing in that provision describes a peptide intended for administration ². A research-use-only vial label is therefore a supplier's statement, not FDA-reviewed labeling, and it does not contain an FDA-reviewed indication, a boxed warning or a clinical adverse-reaction table, because those elements belong to the labeling of approved drugs ¹.

In a 2024 warning letter to a chemical supplier, the agency stated that despite statements on product labeling marketing the products for "research use only" and "not for human consumption", evidence from the website established that the products were intended as drugs for human use ⁵. A 2026 letter to another peptide seller repeated the point in a footnote ⁶. These documents concern the sellers' conduct and claims, not the chemistry of any compound ^5,6.

What a vial label can and cannot tell you

A vial label can establish identity claims, quantity and lot number. It cannot by itself show purity, sequence identity, endotoxin level or net peptide content, which require an analytical certificate from the batch, typically HPLC purity, mass-spectrometry identity and a stated net peptide content. A label also cannot supply human safety information, and absence of an adverse-reaction table should not be read as absence of adverse reactions.

Key points

• FDA prescribing labels follow a regulated structure that includes a boxed warning when required, indications, warnings and adverse-reaction tables ¹.
• Adverse-reaction tables report trial frequencies against placebo, such as nausea in 44% versus 16% in the Wegovy label, and warn against cross-trial comparison ³.
• The "research use only" statement in 21 CFR 809.10 applies to in vitro diagnostic products in the research phase ².
• FDA has stated that research-use-only wording does not change the assessment when evidence shows products are intended as drugs for human use ^5,6.