How FDA Drug Approval Works

Understanding the approval pathway is the fastest way to calibrate any claim about a peptide, because each stage corresponds to a specific question, and knowing which questions have been answered tells you what can honestly be said.

Before humans: preclinical

Laboratory and animal work establishes that a compound does something, characterises how it is absorbed and eliminated, and looks for toxicity across a range of doses.

This stage produces the large majority of the published literature on most research peptides — and it is the stage with the weakest predictive value. The attrition between promising animal results and successful human trials is severe.

Investigational New Drug application

Before a compound can be given to people in the United States, the sponsor files an IND containing the preclinical data, the manufacturing process, and the proposed clinical protocol. FDA has thirty days to object.

Filing an IND is the point at which a compound becomes investigational in the regulatory sense. It is also the point at which most research-chemical compounds diverge permanently from the medicines pathway: they never have a sponsor, so they never have an IND.

Phase 1 — is it tolerable, and what does the body do to it?

Small studies, typically 20–100 participants, usually healthy volunteers. The endpoints are safety, tolerability and pharmacokinetics. Doses escalate cautiously.

Phase 1 is not designed to show that a drug works. The published CJC-1295 human data is Phase 1 work: it established that the compound raises growth hormone and IGF-1 for days, which is a pharmacological finding, not a clinical one.

Phase 2 — does it do anything, and at what dose?

Hundreds of participants who actually have the condition being targeted. Phase 2 establishes dose-response and looks for a signal of efficacy, usually against surrogate or intermediate endpoints.

Most failures happen here. The ipamorelin postoperative ileus trial is a clean example: adequately designed, properly randomised, placebo-controlled, and negative on its primary endpoint.

Phase 3 — does it work, in a population large enough to be sure?

Large randomised controlled trials — often thousands of participants, sometimes tens of thousands — against pre-specified clinical endpoints, with statistical analysis plans fixed in advance.

Phase 3 is expensive because it has to be. It is where effects large enough to matter are separated from effects small enough to be noise, and where adverse events too uncommon to appear in Phase 2 become visible.

New Drug Application and review

The sponsor submits everything: all trial data, the full manufacturing and quality package, and proposed labelling. FDA reviewers analyse the raw data independently rather than accepting the sponsor's analysis. Advisory committees may be convened.

The outcome is approval with a defined label, a Complete Response Letter requiring more work, or refusal.

The label is the output

What emerges is not a verdict that a drug is "safe and effective" in the abstract. It is a document specifying:

• the exact indications, populations and doses studied;
• contraindications;
• warnings and precautions, including boxed warnings;
• adverse reaction rates from the trials;
• drug interactions;
• Limitations of Use — what the drug is not indicated for.

That last section is the most underread document in medicine. The tesamorelin label states plainly that the drug is not indicated for weight loss management and that long-term cardiovascular safety has not been established. Both statements survive in the label because the evidence did not support removing them.

After approval

Phase 4 — post-marketing surveillance — continues for the life of the product. Rare adverse events, long-term effects and interactions that trials were too small or too short to detect emerge here, and labels are revised accordingly.

What this means for unapproved compounds

A compound that has not been through this process has not merely skipped a formality. Nobody has assembled the toxicology package, nobody has established a dose-response relationship in humans, nobody has run a controlled efficacy trial, no regulator has examined the raw data, and there is no surveillance system collecting adverse events.

The absence of an approval is not a gap in paperwork. It is the absence of every mechanism by which a compound's effects in humans become known.