There is controversy over the use and existence of this term. Classically it is believed that with time, a patient becomes accustomed to narcotics and will require an increased dosage. Recent research suggests that this does not occur, and in fact in the long-term, narcotics lower the pain threshold and actually cause pain. This would be consistent with the clinical experience as seen with Heroin addicts. Heroin addicts frequently suffer far worse pain than non-Heroin addicts.