Clinical trials occur in phases.
If a drug makes it through one phase it advances to the next. In general the amount of participants increases with each phase.
Some drugs may undergo up to six years of research in labs, on cells and in animals, before they would even be considered for human clinical trials. This time is known as pre-clinical studies. It tests the drugs in a wide variety of doses and tries to determine which drugs will be effective.
Clinical trials are classified in four phases, phase I – phase IV. There is also a phase 0 which only uses ten to 15 participants. Drugs are given in extremely small amounts with the goal of testing the safety.
Phase I clinical trials generally involve 20 – 100 participants. The dosage of a drug is slowly increased with the goal of determining safety, toxicity and therapeutic levels of the drug. Phase I trials are often conducted on healthy people who are kept under close observation the entire time they are on the medication.
If a drug makes it to Phase II clinical testing, it is now being tested on 20 – 300 participants. This phase will determine how well the drug actually works and what the best dose is going to be. If a drug makes it through phase II and enters a phase III clinical trial there can be 300 – 3,000 participants.
Phase III trials are randomized, controlled and often take place across several facilities. The goal of Phase III is to determine if the new treatment is better than the best treatment currently available. At the end of a phase III trial a “regulatory submission” is prepared.
At this point the drug may even be marketed to the public. Once approved a drug enters Phase IV clinical testing, also known as the Post Marketing Surveillance Trial. During this phase the drug is studied for its interaction with other medications.