Botulinum toxin (Botox) for chronic migraine

Botulinum toxin (Botox, onabotulinumtoxinA) is a preventive treatment approved specifically for chronic migraine: headache on 15 or more days per month for more than 3 months. It is given as an outpatient procedure following the PREEMPT protocol — small injections at defined points across the forehead, temples, back of the head, neck and shoulders — and is repeated every 12 weeks. In clinical trials it significantly reduced the number of headache days per month. It is not for every kind of headache: the first step, always, is confirming the diagnosis.

What chronic migraine is

Migraine is a throbbing headache, usually on one side of the head, of moderate to severe intensity, often accompanied by nausea and sensitivity to light or sound. We speak of chronic migraine when that headache occurs on 15 or more days per month for more than 3 months, with migraine features on at least 8 of those days. That is how the International Classification of Headache Disorders (ICHD-3) defines it, and the threshold is not a technicality: it separates two conditions that are treated differently.

This point matters because botulinum toxin is approved specifically for the chronic form. If you have episodic migraine — intense attacks, but on fewer than 15 days a month — you have other tools, starting with well-chosen preventive medication. And there is a third player we always need to look for: medication-overuse headache, which develops when the very pain relievers a patient takes for relief end up perpetuating the pain. Telling these conditions apart completely changes the strategy. I devote a full article to this topic: chronic headaches: when to see a pain specialist →

I am an anesthesiologist with postgraduate training in Pain Medicine and Interventional Pain Management, and many of the chronic migraine patients I see come to me after years of half-finished treatments. The first thing I do is not to schedule a procedure: it is to rebuild the story. How many days a month it hurts, how many pain relievers you are taking, what the attacks feel like, what sets them off. Many diagnoses change simply by listening carefully to that story, and whether botulinum toxin is indicated depends entirely on that first step.

What botulinum toxin is and how it works

Botulinum toxin type A — the brand studied in the migraine trials is Botox, whose active ingredient is onabotulinumtoxinA — is a protein that, injected in very small doses at precise points, temporarily blocks the release of mediators from nerve endings in the treated area. In chronic migraine, that effect is thought to reduce the sensitization of the pathways that trigger and sustain the attacks. It is the same molecule known for its cosmetic use, but the treatment is a different one: different doses, different sites and a defined medical goal.

Two things I always make clear at the consultation. First: this is a preventive treatment, not a rescue pain reliever; it does not stop today's attack — it aims to make attacks less frequent. Second: the toxin treats the pain, it does not cure migraine. The migraine predisposition is still there; what we are after is lowering the frequency and intensity to give you back days of normal life.

Who I recommend it for (and who I don't)

The typical candidate is a patient with chronic migraine confirmed by formal criteria — headache on 15 or more days per month — who has not achieved adequate control with the usual measures, or who cannot tolerate oral preventive medication. In headache care I work alongside neurology, not instead of it: many of these patients are referred by their neurologist, and others leave my office with a referral arranged.

And who is it not for? Anyone with episodic migraine, pure tension-type headache or another kind of headache that does not meet criteria for chronic migraine. For those conditions there are options with better supporting evidence: preventive medication, greater occipital nerve blocks, injection of cervical trigger points when there is a muscular component — myofascial pain in the upper trapezius, for example, is a frequent cause of tension-type headaches. You can see the full range of procedures on the services and treatments page.

If there is one thing I have learned in this field, it is that choosing patients well is worth more than treating many. When a patient asks me for "the Botox" because a relative had it and did wonderfully, my first task is to verify whether their condition really is chronic migraine. If it is not, the toxin has far less chance of helping them, and there are more appropriate options for their case. Saying "this is not for you, but this other approach is" is also treating pain.

What the treatment is like: the PREEMPT protocol

The injections are not placed by eye: they follow the PREEMPT protocol, the standardized scheme used in the clinical trials that led to the treatment's approval. It consists of 155 units distributed across 31 injection sites over 7 muscle groups of the forehead, temples, back of the head, neck and shoulders, with the option of adding extra sites — up to 195 units — following the areas where each patient's pain predominates.

In practice it is a brief outpatient procedure, performed with a very fine needle, and the discomfort is mild and short-lived. The cycle is repeated every 12 weeks, because the toxin's effect is temporary and the benefit is sustained by staying on schedule.

As for safety, the most frequent adverse effects in the trials were local and transient — neck pain or discomfort, localized muscle weakness in the injected area and, less often, a temporary drooping of the eyelid. Like any intervention, it requires a prior evaluation visit and written informed consent.

What results to expect, according to the studies

Here I prefer to be concrete, because this is where the treatment gets oversold the most. The core evidence comes from two randomized, placebo-controlled clinical trials, PREEMPT 1 and PREEMPT 2, published in 2010, which enrolled chronic migraine patients with nearly 20 headache days per month. In the pooled analysis of both studies, at 24 weeks — that is, after two treatment cycles — patients treated with the toxin had an average reduction of 8.4 headache days per month, versus 6.6 days in the placebo group. In PREEMPT 2, the reduction was 9.0 days versus 6.7 with placebo.

Let's read those numbers honestly. The total improvement is large — going from 20 days of pain to 11 or 12 changes a life — but part of that improvement also occurred in the placebo group; the advantage attributable to the toxin is, on average, real and statistically solid, but moderate. What's more, not every patient responds the same way: some improve far more than the average, and some do not get enough benefit to justify continuing. That is why the sensible approach is to try the full course — the studies assessed results after two cycles — and only then decide together whether it is worth continuing.

And one point I insist on: the toxin does not replace the rest of the treatment. With chronic headaches I work on two fronts at once: the procedure on one side, and on the other, properly chosen preventive medication, managing pain-reliever use when there is overuse, sleep, identifying triggers and managing stress. What defines a good result is not "never having a headache again", but reducing frequency and intensity and getting the predictability of your days back.

When to seek help

A dedicated evaluation is worthwhile if your headaches occur on 15 or more days per month for 3 months or longer, if you have been using pain relievers several days a week on a sustained basis, if the attacks interfere with your work or your sleep, or if you have already tried several preventive treatments without a satisfactory response. At the consultation we confirm the diagnosis, review what has and has not been tried, and decide whether botulinum toxin — or another tool — is the right one for your case.

The plan-by-plan coverage details — OSDE, Swiss Medical, Galeno, Medifé and more — are on the coverage table by procedure →

Where I see patients: locations in Buenos Aires

I see patients at two locations: Hepta, in San Isidro (Av. Fondo de la Legua 577, Zona Norte) and CIAREC, in Villa Urquiza (Av. Monroe 4770, CABA). I receive patients from across Zona Norte (northern Greater Buenos Aires) and the City of Buenos Aires, and I also offer virtual first consultations to point you in the right direction and organize the next steps. Phone: +54 9 11 5895-3260.

Dr. Mauricio Casarsa

Anesthesiologist. Postgraduate training in Pain Medicine and Interventional Pain Management (UBA — Fundación Dolor; UNLP — CAIDBA). Staff physician at Hospital Alemán de Buenos Aires.

MN 137.756 (Argentine medical license) · San Isidro · Villa Urquiza