It's not an easy question. FDA approved Clinical Trials have strict guidelines to protect the welfare of patients:
Clinical Trials and Human Subject Protection If patients meet all the criteria set out in the trial protocols which adhere to FDA guidelines then they can make the decision to enroll or not. For the patient it comes down to weighing options with the advice of physicians. A drug trial involving patients will have met certain criteria for safety in pre-clinical work before clinical work begins. Adverse events in clinical trials vary in severity depending on the condition being targeted and the patient must make the decision to enroll on the basis of options available.
With these factors in mind and given the many medical unknowns of ME/CFS and Fibromyalgia, the biological target of the trial, history of other treatments with the same target and the medical rationale for the trial would factor considerably in the decision.
When all the rational factors are taken into account and risk/reward is assessed the patient must have the conviction and courage to go ahead and enroll.
I have the courage. I would need the conviction, the threshold for which would be fairly low if I knew the risk was high but the trial would help significantly advance understanding of this terribly maddening, debilitating disease.