Each medical research study has its own rules and regulations about who can and cannot take part. These guidelines are called inclusion/exclusion criteria. The inclusion criteria specify characteristics (e.g. age range, health status, severity of symptoms, medications you are currently taking) of people who qualify for participation. Exclusion criteria are in place to protect study participants who may not be compatible with the study therapy. The FDA has very strict requirements that specify which studies involve healthy volunteers and which studies involve patients with the condition being studied.