I participated in some clinical trials (only currently marketed drugs) and they have to watch how long the drug stays in the organism before being eliminated so they take a blood draw every 2 min, than every 30 min, etc. Sometimes they took more than what the donners give to the Red Cross when collecting blood. I never had problems, just sometimes headaches and feeling tired. But there was always one or two participant that felt dizzy and had to rest on a medical chair but it's only due to anxiety.

Frankie