I've been in several clinical trials but none for PH. I had a wonderful experience in all of them. You will find that everything is explained completely. There are many opportunities to ask questions. The trials I've been in have been very well run. Depending on the clinical trial, you may not know if you are in the group that got the placebo or the drug under study. In some trials, there are different strengths of the drug under study. It just depends on the study. All of this info is given to you verbally and in writing. Listen and ask questions.