How many headache days a month is chronic migraine

The definition in the classification

Doctors define chronic migraine using the International Classification of Headache Disorders, third edition (ICHD-3), published by the International Headache Society. Its description of chronic migraine reads: "Headache occurring on 15 or more days/month for more than 3 months, which, on at least 8 days/month, has the features of migraine headache."

The formal criteria have four parts. A: headache, either migraine-like or tension-type-like, on 15 or more days a month for more than 3 months. B: the person has had at least five attacks that meet the criteria for migraine without aura and/or migraine with aura. C: on 8 or more days a month for more than 3 months, the headache meets the migraine criteria, or the person believed it was migraine when it started and it was relieved by a triptan or an ergot derivative. D: it is not better accounted for by another ICHD-3 diagnosis.

"Features of migraine" has a specific meaning. For migraine without aura, ICHD-3 asks for at least two of four characteristics: pain on one side, a pulsating quality, moderate or severe intensity, and pain made worse by routine physical activity such as walking or climbing stairs, or causing you to avoid it. During the headache there must also be nausea and/or vomiting, or sensitivity to both light and sound.

What counts as a headache day

The count is days with any headache, not only migraine attacks. ICHD-3 explains that in people with such frequent headaches it is impossible to tell individual episodes apart, so attacks with and without aura are both counted, as are migraine-like and tension-type-like headaches. Headaches caused by something else, which the classification calls secondary headaches, are not counted.

An attack that runs into a second day makes two headache days. The American Migraine Foundation (AMF) gives an example: if you have a migraine attack with a severe headache on day one, take medication, and still have a low-level headache on day two, that is one day of migraine headache and one day of other headache.

This is where memory lets people down. The AMF notes that many people underestimate their headache days because they count the really bad ones and discount the rest, and warns that reporting only your most severe headaches can give your doctor a false impression of your headache burden, so that a chronic migraine diagnosis might be missed.

Episodic and chronic, and why the line matters

The AMF describes episodic migraine as 14 or fewer headache days a month. It says chronic migraine affects 3 to 5 percent of the US population, and that studies suggest about 3 percent of people with episodic migraine move to chronic migraine each year.

The threshold of 15 days is a classification line, not a measure of how hard your life is. The AMF reports a study in the journal Headache, using data from its American Registry for Migraine Research, which found that people with 8 to 14 headache days a month had similar levels of disability to people with 15 to 23. Even so, the AMF says that frequency is very important for choosing which treatment options to pursue, which is why doctors ask for the number.

Medicine days are part of the picture

ICHD-3 notes that the most common cause of symptoms suggestive of chronic migraine is medication overuse, and that around 50 percent of patients who appear to have chronic migraine revert to an episodic type after the overused drug is withdrawn. People who meet the criteria for both chronic migraine and medication-overuse headache are given both diagnoses.

Medication-overuse headache is defined in ICHD-3 as headache on 15 or more days a month in someone with a pre-existing headache disorder, with regular overuse of acute headache medicine for more than 3 months. The thresholds are counted in days of use per month: 10 or more days for triptans, and 15 or more days for non-opioid painkillers such as paracetamol, aspirin and other NSAIDs. The UK's NICE guideline uses the same lines: 10 or more days a month for triptans, opioids, ergots or combination painkillers, and 15 or more days for paracetamol, aspirin or an NSAID, for 3 months or more. ICHD-3 itself notes that these numbers rest on expert opinion rather than formal evidence.

The NHS puts the everyday version more simply, advising people with migraine to try not to take painkillers for more than 2 days a week, because doing so can cause more headaches. If you are near any of these numbers, the next step is a conversation with your doctor, not stopping a prescribed treatment on your own.

How to count your own days

1. Mark every day on which you had any headache, however mild. A two-day attack is two days.
2. On each headache day, note what it was like: one side or both, throbbing or pressing, how bad, and whether you had nausea, vomiting, or sensitivity to light and sound. Your doctor uses this to judge which days had migraine features.
3. Mark every day you took acute medicine, and which medicine it was.
4. Total each month, and keep going for at least three months, since the definition asks for more than three. ICHD-3 says frequent headaches generally need a day-by-day diary for at least one month before they can be characterised at all.

Then take the counts to your doctor. Criterion D exists for a reason: the AMF says frequent headaches need careful assessment to rule out other causes, including secondary headaches, chronic tension-type headache, hemicrania continua and new daily persistent headache.

Common counting mistakes

Counting attacks instead of days. Five long attacks can add up to ten headache days. The definition is about days.

Leaving out the milder days. Tension-type-like days count toward the 15. Forgetting them is the underestimate the AMF warns about.

Forgetting medicine days. A count of headache days without the matching count of medicine days leaves out half of what ICHD-3 asks your doctor to consider.

Reading the number as a diagnosis. Fifteen headache days a month is where the question starts, not the answer. Criteria B, C and D need a clinician. A diary app can help with the arithmetic: MigrainePage's calendar shows headache days and medicine days for each month as plain numbers, and does not tell you whether you meet any definition.

This guide explains a published classification and is not medical advice. Do not start, stop or change medicine based on a day count; talk to your doctor. The NHS advises calling 999 for a headache that comes on suddenly and is extremely painful.

Frequently asked questions