Clinical trials are carried out to test the therapeutic effects of new drugs and to ensure that they have no unacceptable side effects. Clinical trials can be divided into four phases. Phase I clinical trials are usually carried out on healthy human volunteers to provide a preliminary evaluation of the drug’s safety, its pharmacokinetics and the dose levels that can be administered, but they are not intended to demonstrate whether the drug is effective or not. Bio-equivalence studies are required when different dosage forms are to be used in the early and late phases of clinical trials. Phase II studies are carried out on patients suffering from the condition that the drug is meant to treat. Phase III studies can be divided into phases IIIa and IIIb, and may begin before the end of phase II studies. Phase IV studies are performed after the regulatory authorities have granted market approval for the drug.