When I was on the faculty at the University of Pittsburgh School of Medicine, some of my research regarding the effectiveness of medication for ADD/ADHD utilized a single subject research design. This design uses each person in the study as their own control. This helps eliminate the uncontrolled variables in large n [number of subjects in the study] studies. It does require that the treatment or intervention be reversible quickly. Medication treatments for ADD/ADHD are quickly reversible.
So why have I been talking about this? I have seen how my patients can assess their responses to medication treatments using a single subject research design. They can compare their symptoms before and after treatment. They can then compare their responses by changing the treatment by either changing doses or stopping and restarting the medication. This can be valuable in helping assess the efficacy of medication treatment. It also empowers patients to be more responsible for their treatments and shows them that their input counts.
This methodology can also be used by patients to help them to assess their responses to other forms of treatment such as relaxation and meditation, some cognitive interventions, diet changes, etc.