Is your CGRP working? Count your migraine days before and after.

How do you know if your CGRP medication is working?

Count your migraine days. Take your monthly number from before you started, compare it with the monthly number after three months on the medication (six months if you get a dose every quarter), and look at how big the drop is. The American Headache Society's consensus statement treats a cut of 50% or more in monthly headache days as a clear sign of benefit. It also accepts a meaningful improvement on validated disability scores.

How you feel this week is a poor guide. A hard month after a good one can make a working drug look useless, and the reverse happens just as often.

So the answer is a number you can write down. Most people never write it down, and that's why the question feels impossible six weeks in.

The before-and-after count, worked through

The method has three parts. First, a baseline: your migraine days per month before the first dose, averaged over the one to three months before you started if you can. Second, the same count for every month on treatment. Third, the percentage change, which is baseline minus current, divided by baseline.

Here's how that looks with illustrative numbers. Say you averaged 14 migraine days a month before starting. Month one comes in at 12, month two at 9 and month three at 6.

Taken alone, month one says the drug barely did anything. Month three shows 57% fewer days, which clears the 50% bar. If you'd judged the drug at week five, you'd have dropped a response that was still building.

Count your acute-medication days (triptans, gepants, NSAIDs) alongside your migraine days. Needing fewer rescue doses each month is evidence too, and your neurologist will want to see it.

No baseline? You can rebuild one. Pharmacy refill dates for your acute meds, sick days in your calendar and texts cancelling plans will give you a rough count for the months before you started.

What counts as "working," according to the guidelines

The American Headache Society's 2021 consensus update on preventive treatment sets out what benefit from a CGRP monoclonal antibody looks like, and there's more than one way to meet it. The headline measure is a 50% drop in monthly headache days. The statement also counts a clinically meaningful improvement on validated scores that measure how much migraine takes out of your life. That matters if your day count fell by less than half but your worst days became shorter and milder.

Before the review appointment, ask your neurologist which measure they'll use. If it's MIDAS or HIT-6, fill in the questionnaire at baseline and again at month three, and bring both.

Give it three months before you decide

The consensus timing is three months for antibodies dosed monthly and six months for those dosed quarterly. The window is that long because response often builds. Some people notice a change in month one and plenty don't, so judging at month one cuts the trial short.

Some people respond even later. Real-world cohorts have described late responders who missed the bar at month three and cleared it afterwards Barbanti et al. (2024) studied 572 migraine patients completing ≥48 weeks of anti-CGRP mAb treatment, finding 60.5% (346/572) were responders, with a further group identified as late responders. ([source](https://link.springer.com/article/10.1007/s00415-023-12103-4)). Talk that through with your neurologist, monthly counts in hand, before you switch.

While it's happening, write down the context: a new job, a change in your cycle, a stretch of bad weather, a dose that went in late. A month that looks like failure sometimes has a reason, and by month three you won't remember what it was.

Why the count is also your paperwork

The before-and-after count has a second use. CGRP preventives usually need prior authorization, and renewals often ask for documented improvement. A month-by-month tally against a baseline is that documentation. A note that says "it seems to help" carries much less weight.

We built Postdrome around that gap. You log each attack (in Aura Mode when the screen is hard to look at) and the after-phase days that follow, and the app counts your migraine days per month. When the review appointment or the reauthorization request comes up, you export the count. Your data stays on your phone until you decide to send it somewhere.

If your plan wants justification right now, those numbers are what you build the letter from. Bring the export to your prescriber and let the count do the talking.

When to call before the three months are up

If something new shows up, don't wait for the review window. Call your neurologist sooner for a headache that feels different from your usual attacks, new neurological symptoms like weakness or speech changes that aren't part of your known aura, or signs of an allergic reaction. For the worst headache of your life, or one that reaches full force within a minute, get emergency care.

Erenumab's US label carries warnings for constipation with serious complications and for high blood pressure. It's reasonable to raise new or worsening versions of either on any CGRP preventive. And if two counted months come in worse than your baseline, bring that data in early.