Can I participate in more than one clinical trial at a time?
Generally, no. Almost every protocol's exclusion criteria prohibit concurrent enrollment in another interventional trial. The reason is both scientific and safety-driven: when two investigational treatments interact, neither sponsor can confidently attribute results to their drug, and the participant faces unknown compound risks. There are narrow exceptions — for example, an observational study (which collects data but doesn't change your care) can sometimes run alongside an interventional study, or a long-term follow-up extension of a completed trial may overlap with a new study at the same site. You also typically need to wait 30 days to several months after finishing one trial before joining another, called a 'washout' period. Always disclose every study you've recently been in to the research coordinator — sites verify recent enrollment through ClinicalTrials.gov and screening labs, and undisclosed concurrent participation can disqualify you and put your health at risk.