Tirzepatide's route from laboratory candidate to a drug prescribed to millions is a useful, concrete illustration of what "FDA approval" actually requires, a process that looks nothing like how most research-chemical peptides reach the market.
Preclinical Work
Before any human testing, a candidate compound goes through extensive laboratory and animal studies evaluating basic safety, how it's absorbed, metabolized, and cleared, and whether it shows the intended biological effect. This preclinical package has to satisfy the FDA before an Investigational New Drug (IND) application is even approved to begin human trials.
Phase 1, 2, and 3 Trials
Phase 1 trials, typically involving dozens of healthy volunteers, focus primarily on safety and dosing. Phase 2 trials, with a few hundred participants, start evaluating efficacy alongside safety in the target patient population. Phase 3 trials are the large, often multi-thousand-participant, randomized controlled studies, tirzepatide's SURPASS trials for diabetes and SURMOUNT trials for weight management among them, that provide the statistical evidence regulators actually rely on to evaluate a new drug application.
Regulatory Review
Once trials are complete, the manufacturer submits a New Drug Application (NDA) containing the full trial data, manufacturing process details, and proposed labeling. FDA reviewers, including statisticians and clinical experts independent of the company, evaluate whether the evidence supports the claimed benefits and whether those benefits outweigh documented risks. This review can take many months and frequently involves additional questions sent back to the manufacturer before a decision is reached.
Post-Approval Monitoring
Approval isn't the end of the process. The FDA requires ongoing adverse event reporting, and can mandate additional post-market studies or add new warnings, including boxed warnings, if new safety signals emerge after a drug reaches widespread use. This continued surveillance is part of why an approved drug's label can change years after launch.
Why This Matters for Comparison
This entire process, preclinical work, three phases of increasingly large human trials, independent regulatory review, and ongoing post-market monitoring, is what "FDA-approved" actually represents. It's a genuinely high bar, involving years of work and typically hundreds of millions of dollars in trial costs. That's the standard against which any peptide marketed without it should be honestly measured.
The Cost and Time Involved
Industry estimates for bringing a new drug from initial discovery through FDA approval commonly run into the hundreds of millions of dollars and a decade or more of development time, though estimates vary by methodology and drug class. That scale of investment is itself a filter, only compounds with substantial commercial backing and a credible efficacy signal tend to make it through the full process, which is part of why so many other peptides remain confined to smaller, less rigorous studies indefinitely.