How the FDA Drug Approval Process Works
- Márcio
- Feb 25
- 3 min read
Exterior view of FDA headquarters. Photo credit: Grandbrothers
As we approach February 28, 2025, World Rare Disease Day, the spinocerebellar ataxias community is eagerly awaiting the FDA's ruling on Biohaven's drug Troriluzole. Similarly, people with Friedreich's ataxia are awaiting the FDA's ruling on PTC Therapeutics' drug Vaquitinone.
Let's see how this approval process works.
To obtain FDA approval to market new drugs in the United States, pharmaceutical companies follow a process called a New Drug Application (NDA). This process aims to ensure that new drugs are effective and safe before they are released for sale to the public.
After years of research and testing (when the company believes it has collected sufficient data), it can submit an NDA to the FDA. After receiving an NDA, the FDA conducts a "filing" review to verify that the documentation is complete and suitable for review. If information is missing or contains errors, the FDA can issue a "refusal to file," requesting that the company supplement or correct the application.
This recently happened with Biohaven, which in 2023 had its NDA denied by the FDA for the drug Troriluzole for spinocerebellar ataxias. Specifically, the FDA informed Biohaven that it would not review the NDA for Troriluzole because "the primary objectives of the Phase 3 study conducted in 2023 had not been met," and therefore a proper review would not be possible. Biohaven then collected more data showing "reduced disease progression" and filed a new application in September 2024, which was accepted by the FDA earlier this month (February 2025), and therefore Troriluzole is now under review.
How long does it take for FDA approval?
The timeframe the FDA has to evaluate a New Drug Application (NDA) depends on the type of review the application receives. For Standard Review, the timeframe is 10 months. For Priority Review, the FDA has six months from the date the NDA was accepted to issue its opinion. This type of review is granted to drugs that may offer significant improvements in the treatment of serious diseases. In the case of Biohaven's Troriluzole, the FDA granted Priority Review, meaning the decision must be made within six months of the NDA's acceptance in February 2025, that is, by the third quarter of 2025.
Once the FDA agrees to review an NDA application, it will conduct a thorough evaluation of the submitted data. It will review clinical trial results to confirm efficacy and safety, evaluate how the drug will be manufactured, labeled, and used, evaluate the ingredients, and assess potential side effects. In short, it will conduct a comprehensive analysis.
What are the possible outcomes of the review?
After reviewing an NDA, the FDA can approve the NDA (authorizing the marketing of the drug in the American market), deny the NDA (if it believes there are risks to the health of consumers, in which case the drug cannot be marketed), or may request more information, through a CRL (Complete Response Letter), a "letter" that is sent to the pharmaceutical company requesting more data, and so the pharmaceutical company can provide additional information to support a new review.
Even after a drug or therapy is approved, the FDA continues to monitor its use to ensure safety. Pharmaceutical companies must collect data on the drug already on the market in a Phase 4 clinical trial (Phase IV) to assess side effects and, if necessary, make adjustments to the labeling.
This entire process of evaluating and approving a new drug by the FDA is quite thorough and time-consuming, as many tests are carried out and all documentation is checked to ensure safety and effectiveness before the drug can be purchased by the public.
For more information on NDAs, see the FDA website at
