8. Headache attributed to a substance or its withdrawal

Primary or secondary headache or both?
When a headache occurs for the first time in close temporal relation to exposure to or withdrawal from a substance, it is coded as a secondary headache attributed to exposure to or withdrawal from that substance. This remains true when the new headache has the characteristics of any of the primary headache disorders classified in Part One of ICHD-3 (beta). When a pre-existing headache with the characteristics of a primary headache disorder becomes chronic, or is made significantly worse (usually meaning a two-fold or greater increase in frequency and/or severity), in close temporal relation to exposure to or withdrawal from a substance, both the initial headache diagnosis and a diagnosis of 8. Headache attributed to a substance or its withdrawal (or one of its subtypes) should be given, provided that there is good evidence that exposure to or withdrawal from that substance can cause headache.

Introduction
People with 1. Migraine are physiologically and perhaps psychologically hyperresponsive to a variety of internal and external stimuli. Alcohol, food and food additives, and chemical and drug ingestion and withdrawal, have all been reported to provoke or activate migraine in susceptible individuals. The association is often based on anecdotal data and reports of adverse drug reactions. The fact that these stimuli are associated with headache does not prove causation or eliminate the need to consider other aetiologies. Because common events happen commonly, the association between a headache and an exposure to a substance may be mere coincidence. Headache can occur on the basis of chance. Headache can be a symptom of a systemic disease, and drugs given to treat such a condition will be associated with headache. In acute migraine drug trials, headache, as well as associated symptoms, is listed as an adverse drug reaction despite that it is a symptom of the treated disorder and not the result of treatment. Some disorders may predispose to drug-related headache. Alone, neither the drug nor the condition would produce headache.

The general criteria for the headache disorders listed here are:
A. Headache fulfilling criterion C
B. Use of or exposure to a substance known to be able to cause headache has occurred
C. Evidence of causation demonstrated by two of the following:

    1. headache has developed in temporal relation to use of or exposure to the substance
    2. headache has significantly improved or resolved after removal of the substance
    3. headache has characteristics typical for use of or exposure to the substance
    4. other evidence exists of causation

D. Not better accounted for by another ICHD-3 diagnosis.