Final answer:
A Phase I clinical trial assesses safety, dosage, and side effects by giving a drug to a small group of participants to evaluate its safety profile and establish the range of tolerable doses.
Step-by-step explanation:
A Phase I clinical trial primarily assesses three key variables which are: safety, dosage, and side effects. During this phase, a small group of participants (often healthy volunteers) are given the drug to evaluate the safety profile and to determine the range of doses that should be given. Researchers establish what the drug's most frequent and serious side effects are and, at what dose these effects occur. This initial phase of testing in humans is focused on safety rather than determining how effective the drug is at treating the condition it's supposed to manage.