How the FDA Decides Which Drugs You Can Buy

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Getting a new medicine from a laboratory to your pharmacy involves one of the most demanding regulatory gauntlets in the world. The U.S. Food and Drug Administration oversees this multi-year process with two simple questions: Is this drug safe? And does it actually work?

The FDA operates as a high-stakes gatekeeper, balancing urgent public need for new treatments against the mandate to protect Americans from products that could harm them. This isn’t a single review but a structured, five-stage process that begins with discovery research and ends with lifetime safety monitoring.

Most people never see this process unfold. Yet it determines which treatments reach patients and which promising candidates never make it past the laboratory door.

Discovery and Lab Testing

Finding a Target

The journey starts in laboratories across academic institutions, government facilities, and pharmaceutical companies. Scientists first identify a biological “target” – often a specific protein, enzyme, or DNA sequence that plays a key role in disease.

A target might be a protein on a cancer cell’s surface or an enzyme that helps a virus multiply. Once researchers identify this target, they screen thousands or millions of chemical compounds to find ones that interact with it in potentially helpful ways.

This discovery phase can take years. It’s methodical work that happens far from public view, but it determines which compounds move forward for serious testing.

Safety Testing in the Lab

Once researchers identify a promising compound, it enters preclinical research. The primary goal here is simple: figure out if this drug might seriously harm people.

This phase involves two main types of studies:

In vitro studies happen “in glass” – test tubes, petri dishes, and cell cultures in controlled laboratory environments.

In vivo studies happen “in living” systems – animal models that help scientists understand how complete biological systems react to the drug.

These aren’t informal experiments. The FDA requires all preclinical safety studies to follow Good Laboratory Practice regulations. These strict rules govern everything from facilities and equipment to study protocols and record-keeping.

Scientists need to answer fundamental questions about any drug candidate:

• Pharmacology: What does the drug do to the body?
• Pharmacokinetics: What does the body do to the drug? How is it absorbed, distributed, metabolized, and eliminated?
• Toxicity: Does the drug cause inflammation, organ damage, cancer, or other harmful effects?

Getting Permission for Human Testing

After completing preclinical testing, if data suggests the drug is reasonably safe for initial human use, the sponsor (usually a pharmaceutical company) asks the FDA for permission to begin human trials.

This request comes in the form of an Investigational New Drug (IND) application. The IND isn’t a simple form – it’s a massive document that marks the official transition from lab testing to human research.

The IND application must include:

• Complete results from animal studies showing the drug is reasonably safe for human testing
• Detailed manufacturing information about how the drug is produced, processed, and controlled for quality
• Clinical protocols explaining exactly how, where, and by whom the human trials will be conducted
• Information about the qualifications of clinical investigators
• Official forms including FDA Form 1571 and certification that the trial has been registered with ClinicalTrials.gov

Once the FDA receives the IND, a 30-day review clock starts. If the sponsor doesn’t receive objections within those 30 days, it can legally begin clinical trials. This “silent approval” system is designed for efficiency – it puts the burden on the FDA to identify problems quickly.

The FDA can halt the process by placing the study on clinical hold. This official order delays or stops a proposed trial if the agency has safety concerns or if the application is incomplete. Studies cannot begin until sponsors address all FDA concerns and the hold is lifted.

Human Testing Phases

Once a drug clears the IND stage, it enters clinical trials – the most challenging, expensive, and time-consuming part of drug development. The system works like a funnel with a very high failure rate. Only about 12% of drugs that enter clinical trials ever get approved for public use.

Each clinical trial follows a strict protocol and must be overseen by an Institutional Review Board (IRB) – an independent committee of scientists, doctors, and community members responsible for protecting human research subjects.

The clinical research process typically involves three phases, each designed to answer different questions with increasing numbers of participants.

Phase 1: Safety in Humans

Purpose: Evaluate the drug’s safety in humans. Researchers focus on identifying the most common side effects, establishing safe dosage ranges, and understanding how humans absorb, metabolize, and eliminate the drug.

Participants: Small studies involving 20 to 100 participants. Often these are healthy volunteers, but for diseases like cancer, Phase 1 trials may enroll patients with the condition.

Timeline and Success: Phase 1 trials usually last several months. About 70% of drugs that enter Phase 1 are deemed safe enough to proceed to Phase 2.

Phase 2: Does It Work?

Purpose: The focus shifts to efficacy – does the drug show evidence of working for its intended purpose? Safety monitoring continues, but these studies gather preliminary data on whether the drug has therapeutic effects in people with the targeted disease.

This is a critical “proof-of-concept” stage where many drug candidates fail because they’re not as effective as researchers hoped.

Participants: Larger than Phase 1, enrolling up to several hundred people with the specific condition the drug is meant to treat.

Timeline and Success: These studies last from several months to two years. The odds of success drop significantly – only about 33% of drugs that enter Phase 2 move on to Phase 3.

Phase 3: Better Than Current Treatment?

Purpose: Large-scale, definitive studies designed to confirm the drug’s effectiveness, monitor a wider range of side effects, and compare it to current standard treatments or placebos. These are often called “pivotal trials” because their results form the primary basis for FDA approval decisions.

Participants: The largest and most expensive trials, often involving several hundred to over 3,000 participants across multiple medical centers worldwide.

Study Design: Phase 3 trials are frequently designed as “randomized, double-blind, placebo-controlled” studies – the gold standard of medical research. Participants are randomly assigned to receive either the investigational drug or a placebo, and neither participants nor investigators know who receives which treatment until the study ends.

Timeline and Success: These complex trials take one to four years to complete. The final hurdle is high – fewer than 30% of drugs that make it to Phase 3 ultimately succeed and proceed to FDA submission.

The Failure Funnel

This escalating scale creates what’s essentially a “failure funnel.” The increasing cost, duration, and number of participants at each phase create powerful financial and ethical incentives for drug sponsors to “fail fast.”

It’s far better to discover a drug is ineffective in a smaller, shorter Phase 2 trial than after committing hundreds of millions of dollars and enrolling thousands of patients in a global Phase 3 trial. This structure isn’t a flaw – it’s a core feature designed to efficiently filter out unpromising candidates while minimizing risk to participants.

The entire process generates what the law calls “substantial evidence” of a drug’s effectiveness. The Federal Food, Drug, and Cosmetic Act defines this as “evidence consisting of adequate and well-controlled investigations, including clinical investigations, by experts qualified by scientific training and experience to evaluate the effectiveness of the drug involved.”

FDA Review Process

After successfully navigating three phases of clinical trials, sponsors have gathered what they believe is substantial evidence of safety and effectiveness. The next step is formally asking the FDA for permission to sell the drug to the American public.

Submitting the Application

The formal request takes one of two forms:

New Drug Application (NDA): Used for most new drugs, typically small-molecule chemical entities. The NDA is a massive document, often thousands of pages, meant to tell the “drug’s whole story” from initial discovery through all testing.

Biologics License Application (BLA): The equivalent application for biological products derived from living sources like human, animal, or microorganism cells. This includes vaccines, blood products, gene therapies, and monoclonal antibodies.

Both applications provide the FDA with enough information to make fully informed decisions about safety and effectiveness. The contents are extensive:

• All data from preclinical animal and clinical human studies
• Thorough analysis of the drug’s benefits and risks
• Details on ingredients and manufacturing processes
• Proposed labeling (the package insert that guides physicians and patients on safe, effective use)

Inside FDA Review

Applications land at one of two main FDA centers:

Center for Drug Evaluation and Research (CDER): Regulates most over-the-counter and prescription drugs, including generic drugs and many biological therapeutics. CDER’s oversight extends to products like fluoride toothpaste, antiperspirants, and sunscreens, which are legally classified as drugs.

Center for Biologics Evaluation and Research (CBER): Handles vaccines, blood and blood products, and cell and gene therapies.

The review process follows strict timelines governed by the Prescription Drug User Fee Act (PDUFA). Pharmaceutical companies pay fees that the FDA uses to hire additional staff and conduct timely reviews.

Filing Review (60 Days): The FDA first has 60 days to determine if the application is “sufficiently complete to permit substantive review.” If key components are missing, the FDA can issue a Refuse to File letter, rejecting the application before full review begins.

Substantive Review (6-10 Months): If accepted, the formal review clock starts. For Standard Review, the FDA aims to decide within 10 months. For drugs that appear to represent significant treatment advances, the FDA may grant Priority Review, which sets a 6-month goal.

The review isn’t conducted by a single person but by a multidisciplinary team of FDA experts including physicians, statisticians, chemists, pharmacologists, and other scientists. This team meticulously examines all submitted data.

For particularly novel or controversial drugs, the FDA may convene an Advisory Committee – a panel of independent outside experts providing non-binding recommendations on the drug’s approvability.

The Decision

At the review period’s end, the FDA makes its decision. This isn’t simply about whether the drug works, but whether demonstrated benefits outweigh known risks for the specific population and condition it’s intended to treat.

There are two primary outcomes:

Approval: If the FDA determines the drug is safe and effective and its benefits outweigh risks, the agency issues an Approval Letter. This gives sponsors legal right to market the drug in the United States. FDA-approved labeling becomes the official, legally binding document dictating how the drug can be promoted and used.

Complete Response Letter (CRL): If the FDA determines the application has deficiencies and cannot be approved in its present form, it issues a Complete Response Letter. A CRL isn’t a final rejection – it’s formal communication detailing all specific deficiencies identified by the review team, often including FDA recommendations on how sponsors can address them.

Upon receiving a CRL, sponsors can withdraw the application, request a formal hearing, or work to resolve identified issues and resubmit. Resubmissions are classified by severity: Class 1 resubmissions for minor issues have two-month review goals, while Class 2 resubmissions for substantial issues have six-month goals.

CRLs themselves are confidential and aren’t released publicly because they contain proprietary company information. While companies must disclose CRL receipt to investors, press releases often provide few details about specific reasons for FDA decisions. This creates significant information gaps between companies (which know exactly what’s wrong) and the public and investors (who are often left speculating).

Market consequences can be severe. CRL announcements frequently cause company stock prices to plummet, sometimes by more than 80%.

Fast-Track Programs

While the standard drug review process is methodical and deliberate, the FDA has several special programs designed to get urgently needed drugs to patients faster. These “expedited pathways” are formal regulatory mechanisms created by Congress and the FDA to address serious and life-threatening conditions lacking adequate therapy.

Programs like Accelerated Approval emerged directly from the HIV/AIDS epidemic in the 1980s, when patients and advocates demanded faster access to potentially life-saving treatments.

These pathways represent a shift from one-size-fits-all regulation to a more flexible, risk-based system. The FDA applies different levels of speed and scrutiny depending on disease severity and new drug promise. The greater the unmet need and more compelling the early evidence, the more the FDA is willing to invest resources and accept uncertainty to accelerate patient access.

Fast Track and Breakthrough Therapy

These designations facilitate drug development through enhanced FDA communication.

Fast Track Designation: Intended to facilitate development and expedite review of drugs treating serious conditions and filling unmet medical needs. Sponsors can request Fast Track status early in development, sometimes based on promising preclinical data.

Primary benefits include more frequent FDA meetings to discuss development plans and eligibility for “Rolling Review,” which allows companies to submit completed application sections for review as they become available rather than waiting to submit entire applications at once.

Breakthrough Therapy Designation: This sets a higher bar than Fast Track. To qualify, drugs must be intended to treat serious conditions, and preliminary clinical evidence must indicate they may demonstrate substantial improvement over available therapies on clinically significant endpoints.

Drugs with this designation receive all Fast Track benefits plus more intensive, hands-on FDA guidance on designing efficient drug development programs, including senior FDA manager involvement. The “breakthrough” name can be misleading – designation is based on early evidence and doesn’t guarantee the drug is a true medical breakthrough or will ultimately be approved.

Accelerated Approval

This is one of the most significant and controversial expedited pathways.

The Core Concept: Accelerated Approval allows earlier marketing approval of drugs treating serious conditions and filling unmet medical needs based on surrogate endpoints.

What is a Surrogate Endpoint? A surrogate endpoint is a marker – like a laboratory measurement (lower cholesterol) or physical sign on an X-ray (tumor shrinkage) – thought to be reasonably likely to predict true clinical benefit, like living longer or feeling better, but isn’t the clinical benefit itself. Because surrogate endpoints can often be measured much more quickly than final health outcomes, their use can dramatically shorten clinical trial time.

The Critical Condition: Accelerated Approval is conditional. As a condition of approval, drug sponsors must conduct further post-approval studies, known as confirmatory trials, to verify and describe the drug’s predicted clinical benefit. If these trials fail to show real benefit, or if sponsors don’t conduct them with due diligence, the FDA can withdraw approval.

Controversy and Reform: This pathway has been at the center of public debate, most notably with the 2021 approval of Alzheimer’s drug Aduhelm, which was approved based on its ability to reduce amyloid plaques in the brain (a surrogate endpoint) despite conflicting evidence about clinical benefit.

Critics raised concerns about high prices for drugs with unproven benefits and sponsors failing to complete confirmatory trials in timely manner. In response, Congress passed 2022 legislation strengthening FDA authority, allowing the agency to require confirmatory trials be underway before granting accelerated approval and creating more streamlined procedures for withdrawing drugs if benefits aren’t confirmed.

Priority Review and Vouchers

These mechanisms focus on speeding up the final review phase.

Priority Review: Granted to marketing applications for drugs that, if approved, would represent significant improvement in safety or effectiveness of treating serious conditions. It shortens FDA review goals from standard 10 months to 6 months.

Commissioner’s National Priority Voucher Program: A new initiative announced in 2025 aims for even faster reviews, with goals of one to two months for limited numbers of drugs deemed to align with “U.S. national priorities,” such as addressing health crises or strengthening domestic drug manufacturing. This program utilizes “tumor board-style” team-based review, where experts from across the agency convene simultaneously to increase efficiency.

Comparing FDA Expedited Programs

After Approval: Lifetime Monitoring

A common misconception is that FDA oversight ends once a drug is approved. In reality, FDA oversight continues for the drug’s entire lifecycle. Approval isn’t a final destination but rather a provisional license to enter the market, contingent on the drug continuing to demonstrate acceptable safety profiles in the real world.

The post-market surveillance system acknowledges that full safety and effectiveness profiles can never be completely known from pre-market studies alone. It’s designed to learn and adapt as millions of patients – far more diverse than any clinical trial group – begin using the drug.

Phase 4 Clinical Trials

These studies are conducted after drugs are approved and available to the public. Also known as post-marketing surveillance trials, they can involve thousands of participants and serve several critical purposes:

Fulfilling Requirements: Often conducted to satisfy Accelerated Approval conditions, serving as mandatory confirmatory trials to verify clinical benefit.

Detecting Rare Side Effects: Large, controlled clinical trials conducted for approval may not be large or long enough to detect rare or long-term side effects. Phase 4 trials, which can follow thousands of patients for many years, are better positioned to identify these less common risks.

Studying Real-World Effectiveness: These trials assess how well drugs work in broader, more diverse patient populations, including people of different ages, ethnicities, and those with other medical conditions who may have been excluded from initial trials.

Exploring New Uses: Sponsors may conduct Phase 4 trials to gather data on new indications, different dosages, or drug use in combination with other treatments.

Tracking Problems

The FDA has a robust system for monitoring drug safety on the market, relying on reports from both industry and the public.

Mandatory Reporting: Federal law requires drug manufacturers to review all adverse drug experience information they receive and report serious and unexpected events to the FDA expeditiously.

MedWatch: The FDA’s voluntary safety information and adverse event reporting program. This vital tool allows patients, caregivers, and healthcare professionals to report serious problems they suspect are associated with medical products.

Reports can be submitted online through the MedWatch website or by phone at 1-800-332-1088. They can cover serious adverse events, product quality problems (like defective pills), or medication errors.

FAERS: All reports – both mandatory reports from companies and voluntary reports from the public via MedWatch – are collected in the FDA Adverse Event Reporting System (FAERS). FAERS contains millions of reports and serves as a critical data source for FDA safety experts.

By analyzing FAERS data, FDA scientists can identify potential safety signals – new or emerging patterns of adverse events that might indicate drug problems.

FDA’s Post-Approval Powers

When post-market surveillance reveals new risks, the FDA has a range of regulatory tools to protect the public:

Update Drug Labels: The most common action is requiring manufacturers to update official labeling to include new safety information. This can range from adding new side effects to adverse reaction lists to, in serious cases, adding Boxed Warnings (formerly “black box warnings”) – the FDA’s strongest safety warning used to call attention to serious or life-threatening risks.

Issue Safety Communications: The FDA can issue public drug safety communications to alert patients, healthcare providers, and the public about emerging safety issues.

Require Risk Evaluation and Mitigation Strategy (REMS): For drugs with serious safety concerns, the FDA can require REMS – safety programs that go beyond standard labeling to ensure benefits outweigh risks. These can include requiring special training for prescribers, restricting dispensing to certified pharmacies, or requiring patient monitoring.

Withdraw the Drug: In rare and most serious cases where new risks are so severe they outweigh any benefits, the FDA can remove drugs from the market. This is often done through voluntary recalls by manufacturers in cooperation with the FDA.

Frequently Asked Questions

How can I find out if a drug is FDA-approved?

The best way to verify a drug’s approval status is using the FDA’s official database, Drugs@FDA. This searchable resource contains information on most prescription and over-the-counter drugs approved since 1939. For drugs approved since 1998, you can often find full approval histories, official labeling, and FDA scientific reviews.

What’s the difference between brand-name and generic drugs?

A brand-name drug is the original, innovator product that went through the full, multi-year preclinical and clinical trial process to gain FDA approval via New Drug Application (NDA) or Biologics License Application (BLA).

A generic drug is a copy of a brand-name drug whose patents have expired. Generics are approved through Abbreviated New Drug Applications (ANDA). The application is “abbreviated” because sponsors aren’t required to repeat large and costly clinical trials to prove safety and effectiveness.

Instead, generic manufacturers must scientifically demonstrate their products are bioequivalent to brand-name drugs, meaning they have the same active ingredient, strength, dosage form, and route of administration and work the same way in the body.

Is it legal to import drugs from other countries for personal use?

In most cases, it’s illegal. The Federal Food, Drug, and Cosmetic Act prohibits importing unapproved new drugs into the United States. This includes drugs that may be approved in other countries but haven’t been approved by the FDA.

While the FDA has a policy allowing personnel to exercise discretion under certain circumstances (for example, for serious conditions with no effective U.S. treatment available, and for small, personal supplies), this isn’t a legal right or license for individuals to import drugs. Products remain illegal and are subject to refusal of entry or seizure by the FDA.

For more information, visit the FDA’s Import Program page.

Where can I find information about a drug’s side effects?

The most complete source of information about drug side effects, warnings, and potential interactions is official drug labeling, also known as the package insert or prescribing information. You can request a copy from your pharmacist, find it on drug manufacturer websites, or search for labeling of any approved drug on the Drugs@FDA website.

The FDA also maintains FDALabel, a database allowing full-text searching of drug product labeling.

How do I report a problem with a medication?

If you experience serious side effects or have concerns about medication quality (strange smell or color, broken tablets), report it to the FDA’s MedWatch Program. MedWatch is the agency’s safety information and adverse event reporting program for consumers and healthcare professionals.

You can submit reports securely online or call the FDA toll-free at 1-800-FDA-1088 (1-800-332-1088). Your report can help the FDA identify potential safety issues and protect other patients.

Our articles make government information more accessible. Please consult a qualified professional for financial, legal, or health advice specific to your circumstances.