Individual study sponsors -- including pharmaceutical companies, medical institutions, and foundations -- typically pay for any treatments, special tests, or research costs specific to the clinical trial. However, patients may still be responsible for routine care -- such as doctor visits, hospital stays, and x-rays -- that would be required if they were not part of a trial.
Before you join a trial, always ask which specific medical services, tests and treatments will be covered. Some sponsors will also pay for study-related meals, travel, and housing costs. The clinical trial team should go through the informed consent form with you, which will detail exactly what you have to pay for and what you don't.
If you have health insurance -- including private insurance and government insurance, like Medicare or Medicaid -- ask your benefits provider what costs they will and will not cover.