The ICHD-II diagnostic criteria for MOH:

A. Headache^a present on 15 or more days/month fulfilling criteria C and D.

B. Regular overuse^b for more than 3 months of one or more drugs that can be taken for acute and/or symptomatic treatment of headache.^c

C. Headache has developed or markedly worsened during medication overuse.

D. Headache resolves or reverts to its previous pattern within 2 months after discontinuation of overused medication.

^a The headache associated with medication overuse is variable and often has a peculiar pattern with characteristics shifting, even within the same day, from migraine-like to those of tension-type headache.

^b Overuse is defined in terms of duration and treatment days per week. What is crucial is that treatment occurs both frequently and regularly, i.e. on 2 or more days each week. Bunching of treatment days with long periods without medication intake, practised by some patients, is much less likely to cause medication-overuse headache and does not fulfill criterion B.

^c MOH can occur in headache-prone patients when acute headache medications are taken for other indications.

What medications can cause MOH?
This has long been one of the biggest questions about MOH. There is now sufficient research to address many of our questions. According to Goadsby, et al, "There is now substantial evidence that all drugs used for the treatment of headache may cause MOH in patients with primary headache disorders." When they say, "headache," they mean headache and Migraine both. So, just which medications can cause MOH?

The answer to that question becomes clear when we look at the most recent revisions to The International Classification of Headache Disorders, 2nd Edition (ICHD-II), where we find not only a classification for MOH, but a further breakdown:¹

8.2 Medication-overuse headache (MOH)

8.2.1 Ergotamine-overuse headache
Overuse defined as ergotamine intake on 10 or more days/month on a regular basis for more than 3 months.

8.2.2 Triptan-overuse headache
Overuse defined as triptan intake (any formulation) on 10 or more days/month on a regular basis for more than 3 months.

8.2.3 Analgesic-overuse headache
Overuse defined as intake of simple analgesics on 15 or more days/month^d on a regular basis for more than 3 months.

8.2.4 Opioid-overuse headache
Overuse defined as intake of opioid medications on 10 or more days/month^d on a regular basis for more than 3 months.
Comment:
Studies show that patients overusing opioids have the highest relapse rate after withdrawal treatment.

8.2.5 Combination analgesic-overuse headache
Overuse defined as intake of simple analgesic medicationss^e on 10 or more days/month on a regular basis for more than 3 months.

8.2.6 Medication-overuse headache attributed to combination of acute medications
Intake of any combination of ergotamine, triptans, analgesics and/or opioids on 10 or more days/month on a regular basis for more than 3 months without overuse of any single class alone.^f

8.2.7 Headache attributed to other medication overuse
Regular overuse^g for more than 3 months of a medication other than those described above.

8.2.8 Probable medication-overuse headache

^d Expert opinion rather than formal evidence suggests that use on 15 or more days/month rather than 10 or more days/month is needed to induce analgesic-overuse headache.

^e Combinations typically implicated are those containing simple analgesics combined with opioids, butalbital and/or caffeine.

^f The specific subform(s) 8.2.1–8.2.5 should be diagnosed if criterion B is fulfilled in respect of any one or more single class(es) of these medications.

^g The definition of overuse in terms of treatment days per week is likely to vary with the nature of the medication.