Given the following passage  "In the United States, new pharmaceutical products must be approved by the Food and Drug Administration (FDA) as being both safe and effective. This process generally involves submission of an Investigational New Drug filing with sufficient pre-clinical data to support proceeding with human trials. Following IND approval, three phases of progressively larger human clinical trials may be conducted. Phase I generally studies toxicity using healthy volunteers. Phase II can include pharmacokinetics and dosing in patients, and Phase III is a very large study of efficacy in the intended patient population. Following the successful completion of phase III testing, a New Drug Application is submitted to the FDA. The FDA review the data and if the product is seen as having a positive benefit-risk assessment, approval to market the product in the US is granted.",  answer the following question. Note that the answer is present within the text.  Question: How do the trials occur?
A:
Following IND approval, three phases of progressively larger human clinical trials may be conducted