Clinical trials involve experimental studies performed on people to evaluate medical or behavioral interventions. There are various phases of clinical trials, from initial microdosing and Phase I safety studies involving a small number of participants, to larger Phase II and III studies evaluating effectiveness. Phase IV studies monitor safety and additional uses after approval. Experimental studies can be randomized controlled trials, which are the gold standard, or non-randomized designs. Randomized controlled trials involve a treatment and control group, while other designs may lack a control or randomization.