I, Monster (1971)

Christopher Lee stars in the Amicus production of "Dr. Jekyll & Mr. Hyde" where the names have been changed to Dr. Marlowe and Mr. Blake. Lee as Dr. Marlowe experiments with intravenous drugs that are supposed to release inner inhibitions. So comes forth Mr. Blake (also Lee) who gets more monstrous with each transformation (physically as well as personality). Peter Cushing plays his friend and colleague, Dr. Utterson.