Developing a new drug takes roughly 10 to 15 years and costs an estimated $879 million per drug when you factor in the cost of all the failed attempts along the way. The process moves through a series of distinct stages, from identifying a biological target in the lab to monitoring the drug’s safety long after it reaches pharmacy shelves. Only about 14% of drugs that enter the first phase of human testing ever make it to approval.
Finding a Target
Every drug starts with a question: what specific process in the body could we intervene in to treat a disease? Researchers look for a biological “target,” usually a protein, enzyme, or receptor that plays a key role in how a disease develops or progresses. Teams comb through scientific literature, genetic databases, and public drug databases to identify promising candidates.
Once a target is identified, it needs to be validated. Researchers have to prove that interfering with this target will actually affect the disease. One of the most common techniques involves using small molecules that temporarily silence specific genes, letting scientists mimic what a drug would do and observe the result. Computational modeling and crystallography (which maps the 3D shape of proteins) help researchers understand how a potential drug molecule might physically interact with the target. This phase can take years of painstaking lab work before a promising compound, sometimes called a “lead,” emerges.
Preclinical Testing
Before any drug candidate touches a human body, it goes through extensive preclinical testing. This stage has three primary goals: determine a safe starting dose for humans, identify which organs the drug might damage, and figure out what doctors should monitor during human trials.
Testing begins with cell cultures in the lab. Researchers expose cell lines to the compound to observe its direct effects on cell behavior and growth, measure how strongly it binds to its target, and confirm it does what it’s supposed to do biologically. These in vitro experiments help scientists pick the right animal species for the next round of testing.
Animal studies typically involve two relevant species and examine the drug’s effects on major organ systems: cardiovascular, respiratory, kidney, and central nervous system function. Researchers run single-dose studies first to understand the relationship between dose and toxicity, then move to repeated-dose studies lasting anywhere from two weeks to three months depending on how long patients would ultimately take the drug. Throughout this process, scientists track how the drug is absorbed, distributed through tissues, and eliminated from the body.
Filing to Begin Human Trials
To test a drug in people, a company must file an Investigational New Drug (IND) application with the FDA. This is essentially a request for permission. Federal law prohibits shipping an unapproved drug across state lines, and since clinical trials involve sending the drug to doctors and hospitals around the country, the IND serves as a legal exemption. The application includes all the preclinical data collected so far, a plan for how human studies will be conducted, and information about the drug’s manufacturing process.
Phase 1: Safety in Healthy Volunteers
Phase 1 trials are small, typically enrolling 20 to 80 people, often healthy volunteers rather than patients. The primary question is simple: is this drug safe for humans? Researchers start with very low doses and gradually increase them, carefully tracking side effects, how the body processes the drug, and what dose range appears tolerable. These trials are closely monitored and move slowly by design.
Phase 2: Does It Actually Work?
If a drug passes Phase 1, it moves into Phase 2 trials with 100 to 300 participants who actually have the disease the drug is meant to treat. The focus shifts to effectiveness. Does the drug improve symptoms? Slow disease progression? Shrink tumors? Researchers also continue studying safety, refining the optimal dose and identifying side effects that only appear in a larger or sicker population. Many drugs fail here. A compound that looked promising in the lab and seemed safe in Phase 1 may simply not work well enough in real patients to justify moving forward.
Phase 3: Large-Scale Confirmation
Phase 3 trials are the big, expensive, decisive studies. They enroll 1,000 to 3,000 participants across multiple hospitals and countries. The goals are to confirm the drug’s effectiveness, compare it against existing treatments or a placebo, monitor side effects in a diverse population, and gather enough data to support a formal approval application. These trials often take several years to complete and represent the largest single investment in the development process.
The sheer size of Phase 3 trials is what makes them so valuable. Rare side effects that didn’t show up in 200 people may appear in 2,000. Effectiveness that looked strong in a carefully selected Phase 2 group may look more modest in a broader, real-world population. Phase 3 results are what regulators ultimately base their approval decisions on.
Applying for Approval
When a company believes it has enough evidence, it submits a New Drug Application (NDA) to the FDA. This is a massive document covering the drug’s chemistry, pharmacology, clinical trial results, statistical analyses, and proposed labeling. FDA reviewers evaluate the data from multiple technical angles. Under standard review, the agency aims to make a decision within about 10 months. Drugs that receive Priority Review, reserved for treatments that offer significant improvements over existing options, get a 6-month timeline.
Some drugs qualify for expedited pathways. Treatments for serious conditions with no good alternatives can receive Accelerated Approval based on surrogate endpoints, meaning a lab measurement or physical sign that’s reasonably likely to predict a real clinical benefit, rather than waiting years to measure long-term outcomes. This is how many cancer drugs and HIV treatments have reached patients faster.
Manufacturing at Scale
A challenge that runs parallel to clinical testing is figuring out how to manufacture the drug reliably at commercial scale. Making a few kilograms of a compound in a lab is fundamentally different from producing tons of it in a factory. Formulation scale-up remains a major hurdle in drug development, partly because early research teams rarely design their formulations with large-scale production in mind. Decisions made early on about ingredients and manufacturing processes can create significant problems later if they don’t translate well to industrial equipment and volumes.
Phase 4: Monitoring After Approval
Approval is not the finish line. The FDA often requires Phase 4 studies as a condition of approval. These post-marketing studies track the drug’s performance in the real world, where patients are older, sicker, and taking more medications than the carefully screened participants in clinical trials. Phase 4 studies can focus on a specific known side effect, overall safety surveillance, long-term effectiveness, or how the drug performs in populations that were underrepresented in trials, including children, elderly patients, pregnant women, and specific racial or ethnic groups.
This ongoing surveillance occasionally reveals problems serious enough to warrant new warnings, restricted use, or in rare cases, pulling the drug from the market entirely.
Why Most Drugs Never Make It
An analysis of nearly 20,000 clinical trials conducted by 18 major pharmaceutical companies between 2006 and 2022 found that only 14.3% of drugs entering Phase 1 trials ultimately received FDA approval. Individual companies ranged from 8% to 23%. The direct, out-of-pocket cost to develop a single drug averages about $173 million, according to a 2024 analysis from the U.S. Department of Health and Human Services. But when you add in the cost of all the drugs that failed along the way and the capital tied up during the long development timeline, that figure rises to $879 million per approved drug.
Failure can happen at any stage and for many reasons: the drug turns out to be toxic, it doesn’t work well enough, it’s no better than what already exists, manufacturing proves impractical, or the company simply runs out of funding. The high failure rate is the central economic reality of the pharmaceutical industry and a major reason new drugs carry steep price tags.