Chronic or episodic migraine? Why 15 days is the line

Chronic migraine is a defined diagnosis, not a description of feeling unwell often: 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, and 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 excluding the “small” ones, and that undercount is the reason many are told they do not qualify for treatments they in fact qualify for.

How episodic becomes chronic

Chronification is not random. The recognized contributors are worth knowing because most are modifiable:

• Medication overuse — the largest single one. See medication-overuse headache.
• Untreated or undertreated attacks, which appear to sensitize the system 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, and it is why counting honestly matters more than it seems.

Acute treatment also changes character. Below the threshold, the priority is treating attacks well. Above it, treating every attack aggressively is part of what sustains the pattern, and 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. Reversion from chronic to episodic is common, particularly when medication overuse is addressed. Many people who arrive counting 20-plus headache days a month are counting far fewer some months later, and 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 criterion 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, which 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. Simplicity matters more than detail — a system you abandon in a week is worse than a tick per day. Bring it in; see contact.

Sources

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