Medication overuse headache

A medication overuse headache (MOH), also known as a rebound headache, usually occurs when painkillers are taken frequently to relieve headaches. These cases are often referred to as painkiller headaches. Rebound headaches frequently occur daily, can be very painful and are a common cause of chronic daily headache. They typically occur in patients with an underlying headache disorder such as migraine or tension-type headache that "transforms" over time from an episodic condition to chronic daily headache due to excessive intake of acute headache relief medications. MOH is a serious, disabling and well-characterized disorder, which represents a worldwide problem and is now considered the third-most prevalent type of headache. The proportion of patients in the population with Chronic Daily Headache (CDH) who overuse acute medications ranges from 18% to 33%. The prevalence of medication overuse headache (MOH) varies depending on the population studied and diagnostic criteria used. However, it is estimated that MOH affects approximately 1-2% of the general population, but its relative frequency is much higher in secondary and tertiary care.

Medication overuse headache is a recognized ICHD (International Classification of Headache Disorders) classification. Over the years different sets of diagnostic criteria have been proposed and revised by the major experts of headache disorders. The term MOH first appeared in the ICHD 2nd edition in 2004. It was defined as a secondary headache, with the aim of emphasising excessive drug intake as the basis of this form of headache. The two subsequent revisions of the diagnostic criteria for MOH (2005 and 2006) refined and extended the definition of the condition on the basis of both its chronicity (headache on more than 15 days/month for more than three months) and drug classes, thereby identifying the main types of MOH. In the case of ergotamine, triptans, opioids and combination medications in particular, intake on > 10 days/month for > 3 months is required, whereas simple analgesics are considered overused when they are taken on > 15 days/month for >3 months.

MOH is known to occur with frequent use of many different medications, including most commonly: triptans, ergotamines, simple and combination analgesics, and opioids. Common over-the-counter medicines that can cause headaches when overused include Excedrin Migraine, Cafergot, and Advil. Dietary and medicinal caffeine consumption appears to be a modest risk factor for chronic daily headache onset, regardless of headache type.

A lifelong history of headaches is a major risk factor for MOH. MOH is very rare in patients without a history of recurrent headaches, and it rarely develops in patients who take analgesics for non-headache pain, like arthritis or irritable bowel syndrome. Furthermore, MOH is more probable when a family history of MOH is present, thus indicating a genetic susceptibility. It is thought that rebound headaches are caused by a neuronal re-adjustment process. Analgesic intake raises the pain threshold. Thus, lacking pain stimuli for longer times, the brain re-calibrates to experience normal stimuli as pain.

The time it takes for someone to develop medication overuse headaches (MOH) after taking medication too often depends on the type of medication they are using. If someone is taking triptans (such as Sumatriptan etc.), it may take about 1.7 years for them to develop MOH. If they are taking ergots (such as Ergotamine etc.), it may take about 2.7 years, and if they are taking analgesics (such as Naproxen etc.), it may take about 4.8 years. So, the delay between taking medication too often and developing MOH varies based on the type of medication being used.

The underlying mechanisms that lead to the development of the condition are still widely unknown and clarification of their role is hampered by a lack of experimental research or suitable animal models. Various pathophysiological abnormalities have been reported and they seem to have an important role in initiating and maintaining chronic headache (genetic disposition, receptor and enzyme physiology and regulation, psychological and behavioural factors, physical dependencies, recent functional imaging results).

In some cases, individuals may be genetically predisposed to developing medication overuse headache. A PET study in patients with chronic analgesic overuse showed decreased activity in the orbitofrontal cortex of the brain, which is also seen in substance abuse. This suggests that there may be an underlying neurological susceptibility to addiction in some individuals. However, more research is needed to fully understand the complex interplay of factors that contribute to the development of MOH.

Opioids and butalbital are sometimes inappropriately used as treatment for migraine and headache and should be avoided in favor of more effective, migraine-specific treatments. Opioid and butalbital use can worsen headaches and cause MOH. When a patient fails to respond to other treatment or migraine specific treatment is unavailable, then opioids may be used.