Some very important medical discoveries and advances are due to self experimentation. An excellent history of this controversial and understudied practice can be found in Lawrence Altman's book "Who Goes First?: The Story of Self-Experimentation in Medicine"
These photos show Werner Forssmann (left) and an X-Ray he took of himself with the first cardiac catheterization performed in a human (right).
The Shulgins brought systematic self experimentation into the study of psychedelics.