An IND is the application to start testing a drug in humans; an NDA is the application to approve a small-molecule drug for sale; and a BLA is the application to approve a biologic for sale. Put simply, the IND opens the door to clinical trials, and the NDA or BLA is what you file at the end to actually market the drug. Which of the latter two you file depends on whether your product is a chemical drug or a biologic. Here is how the three fit together across a drug’s life.
The drug journey, in three gates
Every drug that reaches patients passes through a sequence of regulatory gates, and these three filings mark the most important ones. Think of the journey in order: you discover and test a candidate in the lab and in animals; you file an IND to begin human trials; you run those trials across several phases; and if the data are good, you file an NDA or BLA to win approval to sell. The IND is the entrance; the NDA or BLA is the finish line.
IND: the Investigational New Drug application
Before a company can give an experimental drug to a human being in the US, it must file an Investigational New Drug application with the FDA. The IND is essentially a request for permission to begin clinical trials, backed by the evidence gathered so far. It pulls together the preclinical data (animal safety and pharmacology studies), the manufacturing information showing the drug can be made consistently and safely, and the detailed plan for the proposed clinical trials. The FDA reviews the IND to decide whether it is reasonably safe to proceed and whether the trial design adequately protects the people who will take part. Clear the IND, and human testing can begin. Everything before this point is preclinical; everything after is the clinic.
The trials in between
The IND opens the door to clinical development, which unfolds across phases: small early trials focused on safety, mid-size trials that look for signs the drug works and refine the dose, and large pivotal trials that aim to prove safety and efficacy convincingly. This is the long, expensive, failure-prone heart of drug development. Only if a candidate survives it, generating data strong enough to convince regulators, does a company move to the final filing.
NDA: the New Drug Application (for small molecules)
For a conventional, chemically synthesized small-molecule drug, the final submission is a New Drug Application. The NDA is a massive dossier that assembles everything: all the clinical trial results, the full safety and efficacy analysis, the drug’s chemistry and manufacturing details, the proposed labeling, and more. It is the formal request for the FDA to approve the drug for marketing. The agency reviews it in depth, sometimes convening advisory committees, and either approves the drug, requests more information, or declines. An NDA approval is what allows a small-molecule drug to be sold.
BLA: the Biologics License Application (for biologics)
For a biologic, a large, complex molecule made in living cells, such as an antibody, a vaccine, or a cell or gene therapy, the equivalent final submission is a Biologics License Application. The BLA plays the same role as the NDA, requesting approval to market the product, but it reflects the different nature and regulation of biologics, where the manufacturing process is inseparable from the product itself. A biologic is not “approved” with an NDA; it is licensed via a BLA. This is why you will often hear that a company “filed a BLA” for an antibody but an “NDA” for a pill, the split simply follows whether the product is a biologic or a small molecule.
The three filings at a glance
| Filing | What it does | When | For |
|---|---|---|---|
| IND | Permission to begin human trials | Before clinical testing | Any investigational drug |
| NDA | Approval to market | After successful trials | Small-molecule drugs |
| BLA | License to market | After successful trials | Biologics |
A few related terms worth knowing
The system has other doorways. An ANDA (Abbreviated New Drug Application) is the streamlined pathway for generic small-molecule drugs, which do not need to repeat the original’s trials. A 505(b)(2) application is a hybrid route that lets a developer rely partly on existing data for a modified version of an approved drug. And biosimilars follow their own dedicated pathway rather than a standard BLA. You do not need to memorize these, but knowing they exist helps you place any given filing in context.
Why this matters
These filings are not just paperwork; they are the milestones a whole industry organizes around. An IND clearance means a company can finally test its science in people, often a value-inflection point for investors. An NDA or BLA acceptance and approval can transform a company overnight. When you read that a biotech “filed its BLA” or “received IND clearance,” you now know exactly where that company sits on the long road from laboratory to pharmacy, and how much, or how little, still lies ahead.
What actually goes into these submissions
It is worth appreciating just how large these filings are, because their scale explains a lot about drug-development timelines and cost. A modern marketing application, an NDA or a BLA, is not a document so much as a vast structured dossier, often running to enormous length and organized into standardized sections covering the drug’s chemistry and manufacturing, the preclinical studies, and the full clinical program, along with proposed labeling and risk-management plans. This standardized structure exists so that regulators around the world can review submissions in a consistent format, and assembling it is a major undertaking that pulls in scientists, statisticians, regulatory specialists, and medical writers, often for many months. Once filed, the application enters a formal review with defined timelines, during which the agency may ask questions, request additional analyses, or convene an advisory committee of outside experts to weigh in publicly on whether the drug should be approved. The review ends in one of a few outcomes: approval, or a formal letter identifying deficiencies that must be addressed before the drug can be approved, which can add months or years. The IND, while smaller than a marketing application, follows the same spirit, a structured package of preclinical, manufacturing, and clinical-plan information that the agency reviews before permitting human testing. Understanding this helps explain why regulatory milestones are such significant events for companies: each filing represents an immense, expensive body of work, and each agency decision can validate years of effort or send a program back to the drawing board. When you read that a company has filed or received a decision on one of these applications, you are watching one of the highest-stakes moments in the entire drug-development process.
Why founders should care about sequencing
For company builders, these filings are not just regulatory chores; they are the milestones that create, or destroy, value. Each one is a natural inflection point that investors watch closely. Clearing an IND means you can finally test your science in humans, which de-risks the company and often unlocks the next round of financing. Filing and winning an NDA or BLA can transform a company’s prospects overnight. Because of that, the sequencing and timing of these submissions should be woven into a company’s financing strategy from the start: you want enough runway to reach the next filing milestone with a buffer, because running out of cash just before an IND clearance or a filing decision is a classic and avoidable way to lose leverage. Understanding where these gates sit, and planning your capital and your narrative around them, is a core part of building a biotech rather than just running the science.
For daily coverage of the filings, clearances, and approvals that move companies and markets, the BioMed Nexus brief tracks them as they happen, and the regulatory and compliance directory lists the consultants who help companies prepare and navigate these submissions.
Frequently asked questions
What is the difference between an IND, an NDA and a BLA?
An IND (Investigational New Drug application) is filed to get permission to begin human clinical trials. An NDA (New Drug Application) is filed after successful trials to win approval to market a small-molecule drug. A BLA (Biologics License Application) does the same for a biologic. The IND opens trials; the NDA or BLA seeks final approval.
What is an IND application?
An Investigational New Drug application is a submission to the FDA requesting permission to begin testing an experimental drug in humans. It includes preclinical animal safety data, manufacturing information, and the proposed clinical trial plan. The FDA reviews it to judge whether human testing can proceed safely.
When do you file a BLA instead of an NDA?
You file a BLA (Biologics License Application) for a biologic, a large, complex molecule made in living cells such as an antibody, vaccine, or cell or gene therapy. You file an NDA (New Drug Application) for a conventional small-molecule drug made by chemical synthesis. The filing follows the type of product.
