A Q&A with Jacinta Johnson, B.Pharm
How frequently rebound headaches occur depends on the type and dose of overused drug and the frequency of headaches. What are the differences between the drugs/dose?
There are still a lot of unknowns with regard to which drugs are capable of inducing medication overuse headache in what doses. From the literature it is clear opioids are a particularly problematic class of medications, as they have consistently been associated with progression from episodic to chronic headache, even when initiated for other indications. Use of barbiturates has also come out as a significant risk factor in headache chronification in a large longitudinal study. Overall, non-steroidal anti-inflammatory drugs (NSAIDs) are not associated with transition from episodic to chronic headache, in fact in patients who begin with headaches around up to nine days per month NSAIDs are protective against chronic headache, however in patients with very frequent headaches at baseline NSAIDs can the increase risk of chronic headache. Although many studies report an improvement in headache when overused triptans are withdrawn, prospectively triptans have not been shown to increase the risk of chronic headache.
The specific doses that can lead to medication overuse headache, and conversely those that are safe to consume, are not well established. Often in medication overuse headache studies drug dose in defined in terms of days of intake per month, rather than amount of the drug consumed, thus it may be that the frequency of intake rather than the absolute dose is more important in determining outcome. It has been reported that the critical intake for opioids is around eight days per month, which conflicts somewhat with the arbitrary cut-off of 10 days per month of intake required for an official ICHD-II diagnosis of opioid overuse headache.