FDA-Approved vs. Investigational vs. Research Peptides

The four categories

FDA-approved

An approved drug has completed the full development process:

1. Preclinical studies in the lab and in animals.
2. Phase 1 trials in a small group, usually healthy volunteers, to study safety and how the body handles the drug.
3. Phase 2 trials in a few hundred patients to find the dose and get early evidence of effect.
4. Phase 3 trials in hundreds to thousands of patients to confirm effect and safety against placebo or an existing treatment.
5. FDA review of all of that data, plus inspection of the manufacturing facilities.

Approval means the FDA concluded the drug’s benefits outweigh its risks for a specific use at a specific dose. It comes with prescribing information that lists indications, doses, warnings, and side effects. Semaglutide’s first approval (Ozempic) was in 2017. Tirzepatide’s (Mounjaro) was in 2022.

Approval is use-specific. A drug can be approved for one condition and investigational for another.

Investigational

An investigational drug is one being studied in people under an Investigational New Drug (IND) application filed with the FDA. It has not been approved. That covers everything from a first-in-human study to a drug in late phase 3 with strong results.

Retatrutide is a clear example. It has completed multiple phase 3 trials with large reported weight loss, and Lilly plans to file for approval in early 2027. It is still investigational. Until the FDA approves it:

• It is only available to people enrolled in a trial.
• There is no approved dose, strength, or device.
• The FDA has said it cannot be used in compounding.
• Anything sold online under its name is not the trial drug.

The FDA’s expanded access program can allow investigational drugs for seriously ill patients outside trials, but only with the manufacturer’s agreement and FDA authorization. It is not a route to buying a drug.

Compounded

Compounding is when a licensed pharmacist makes a drug for an individual patient, usually because an approved product does not meet that patient’s needs (an allergy to an ingredient, a different strength, or a shortage). Two legal pathways exist:

• 503A pharmacies compound for specific patients under state board of pharmacy oversight.
• 503B outsourcing facilities can compound larger batches and are registered with and inspected by the FDA.

Compounded drugs are not FDA-approved. The FDA does not review them for safety, effectiveness, or quality before they are sold. A 503A pharmacy may compound only with bulk ingredients that meet a USP or NF monograph if one exists, or, if not, that are part of an FDA-approved drug or on FDA’s 503A bulk substances list. The ingredients must come from an FDA-registered manufacturer with a certificate of analysis.

During the semaglutide and tirzepatide shortages, compounded versions were widely prescribed. The FDA has since declared those shortages resolved and has published policies for compounders. It has also documented safety issues with compounded GLP-1 products, including dosing errors, products made with salt forms of semaglutide, which are different active ingredients from the approved drugs, and products shipped without proper temperature control.

“Research use only”

Under federal law, whether a product is a drug depends on its intended use, not just its label. FDA has issued warning letters to sellers of peptides like semaglutide, tirzepatide, and retatrutide labeled “for research purposes” or “not for human consumption” and sold for people to use. FDA considers these illegal, unapproved drugs.

A “research use only” label does not make a product legal or safe to inject.

What “research use only” means in practice:

• No trial has tested the product in people.
• No regulator has checked what is in the vial.
• No manufacturing standard for human injection applies.
• No label tells you the strength, so no dose math can be trusted.

Why the category matters more than the name

A vial labeled “semaglutide” could be any of the four. The name tells you the molecule the seller claims is inside. The category tells you whether anyone independent has confirmed that claim, whether the product is sterile, and whether the stated strength is real.

The FDA has reported patients who took 5 to 20 times their intended dose of compounded semaglutide because of confusion between milligrams, milliliters, and syringe units. Those products at least had a labeled strength to get wrong. A research vial may not have a verified strength at all.

Quick ways to tell them apart

• A branded pen or vial from a pharmacy with prescribing information: approved.
• A drug you can only get by joining a study: investigational.
• A vial from a state-licensed pharmacy with a patient-specific label and a prescriber’s name: compounded.
• A vial from a website with “research” in the name and no prescriber involved: research use only, and not for people.