Chronic or episodic migraine? Why 15 days is the line

Chronic migraine is a defined diagnosis, not a way of saying you often feel unwell. It means headache on 15 or more days a month for more than three months, with at least eight of those days having migraine features.¹

The line matters because treatment options change on either side of it. It also matters because crossing it is usually a process you can interrupt.

The criteria, precisely

• Headache — of any type — on 15 or more days per month
• Sustained for more than three months
• On at least eight of those days, the headache has migraine features or responds to migraine-specific treatment
• In a person who has had at least five prior migraine attacks

Note that the 15 days counts all headache days, not just migraines. People routinely undercount by leaving out the “small” ones. That undercount is why many are told they do not qualify for treatments they in fact qualify for.

How episodic becomes chronic

Chronification (the shift from episodic to chronic) is not random. The known contributors are worth knowing, because most can be changed:

• Medication overuse — the largest single one. See medication-overuse headache.
• Untreated or undertreated attacks, which appear to make the system more sensitive over time
• Untreated mood and anxiety disorders, which independently predict progression
• Poor or irregular sleep, including undiagnosed obstructive sleep apnea
• Obesity and metabolic factors

That list is also the intervention list. See headache prevention.

What changes at the threshold

Botox is indicated for chronic migraine and not for episodic — the trials in people below 15 days did not show benefit. That is the clearest example. It is why counting honestly matters more than it seems.

Acute treatment also changes. Below the threshold, the priority is treating attacks well. Above it, treating every attack hard is part of what keeps the pattern going. So the plan has to shift toward prevention and toward unwinding rebound.

Chronic is not permanent

The most useful thing to know is that people move back across the line. Going back from chronic to episodic is common, especially when medication overuse is addressed. Many people arrive counting 20-plus headache days a month and, some months later, are counting far fewer. The largest single lever was usually the medicine cabinet rather than a new drug.

The word “chronic” describes your current pattern. It is not a prognosis.

Common questions

Do I count days when the headache was mild?

Yes. The 15-day rule counts headache days of any type and any severity, not just severe migraine attacks. Undercounting mild days is the most common reason people are told they do not qualify. See Botox for chronic migraine.

What if I’m at 12 or 13 days?

Then you have high-frequency episodic migraine. That is the group most at risk of crossing over — and the group where prevention pays off most. See headache prevention.

Can chronic migraine go back to episodic?

Yes, and it commonly does, especially once medication overuse is addressed. See medication-overuse headache.

How do I actually keep track?

A paper calendar with a mark for any headache day and a note of every dose of anything taken. Keeping it simple matters more than detail — a system you abandon in a week is worse than a tick per day. Bring it in; see contact.

Could my daily headaches be rebound headaches?

If you treat headache on 10 or more days a month (15 for plain ibuprofen, aspirin or acetaminophen), there is a real chance. The tell is a headache that is already there when you wake, eases only partly with your usual tablet, and gets worse within hours when you skip a dose. Rebound days count toward the 15-day line, so part of a chronic count can be manufactured by the treatment itself. See how medication-overuse headache is unwound.

Sources

1. Headache Classification Committee of the International Headache Society. ICHD-3, 1.3 Chronic migraine. ichd-3.org