Clinical trials that entail significant costs to participants should generally be avoided. Trials can be inconvenient. They usually require extra visits to the doctor's office or to a clinic or hospital. Some may even require you to be admitted to the hospital for a time. Ask if any of these costs are covered by the trial.
Trials can be unpleasant.
They may require that you undergo a lot of tests, and these tests may be uncomfortable or even painful. It is not uncommon for such studies to require that you have blood samples taken on a regular basis, and some trials may also require stool samples, sputum samples, bone-marrow testing, and other laboratory tests. Although the list of disadvantages is longer than the list of advantages, this does not mean that the scales usually tip against joining a trial. What this does mean is that entering a clinical trial is not a decision that should be taken lightly. Don't sign up on the spur of the moment.