PREEMPT Botox Chronic Migraine Guidelines Explained

What the PREEMPT Trials and Current AAN/AHS Guidelines Actually Say About Botox for Chronic Migraine

A patient sits across from a clinician after months of near-daily headaches that began after a collision or simply worsened over time. Oral preventives have either failed or caused side effects she cannot tolerate. She asks a direct question: “Does the evidence really support Botox for this condition, or is it being used because nothing else is working?” That question is the right one. The answer lives in the PREEMPT trials and the 2026 American Academy of Neurology (AAN) and American Headache Society (AHS) guideline—not in marketing claims or anecdotes.

What the PREEMPT Program Actually Tested

The Phase III Research Evaluating Migraine Prophylaxis Therapy (PREEMPT) program consisted of two multicenter, randomized, double-blind, placebo-controlled trials (PREEMPT 1 and PREEMPT 2). Together they enrolled 1,384 adults who met the definition of chronic migraine: headache on 15 or more days per month for at least three months, with at least eight of those days meeting criteria for migraine (Dodick et al., 2010). Participants received either onabotulinumtoxinA or placebo injections every 12 weeks.

The fixed component used in the trials—and still listed in the U.S. prescribing information—was 155 units distributed across 31 specific sites in seven head-and-neck muscle groups. Those groups are the corrugator, procerus, frontalis, temporalis, occipitalis, cervical paraspinal muscles, and trapezius. Each site received 5 units. The trials also allowed clinicians to add up to 40 additional units in a “follow-the-pain” pattern (temporalis, occipitalis, or trapezius), bringing the maximum to 195 units across up to 39 sites. The current FDA-approved regimen centers on the 155-unit, 31-site fixed map.

Primary endpoints differed slightly between the two trials. PREEMPT 1 used headache episodes and did not meet its pre-specified primary endpoint. PREEMPT 2 used headache days and did. When the double-blind phases were pooled, the results showed a mean reduction of 8.4 headache days per 28-day period with onabotulinumtoxinA versus 6.6 days with placebo at week 24 (difference of 1.8 days; p < 0.001). Secondary measures also favored the active treatment, including reductions in headache severity and improvements on the Headache Impact Test (HIT-6) and migraine-specific quality-of-life scores (Dodick et al., 2010; Blumenfeld et al., related analyses).

Importantly, roughly half of patients achieved at least a 50 percent reduction in headache days by week 24, and more than 70 percent met at least one clinically meaningful responder criterion (headache days, severity, or impact measures). Benefit often continues to accrue with additional cycles. The open-label extension and subsequent long-term studies such as COMPEL showed further average reductions with continued treatment. Most patients are assessed for meaningful response after two treatment cycles—approximately 24 weeks—rather than after the first injection. The 2026 AAN/AHS guideline explicitly recommends waiting 24 weeks at the recommended dose before judging the efficacy of onabotulinumtoxin A for migraine prevention.

Current AAN/AHS Recommendations and the Chronic-Only Boundary

The 2026 AAN/AHS practice guideline on pharmacologic migraine prevention updated earlier guidance after a systematic review of evidence through mid-2024. For adults with chronic migraine, the guideline states that clinicians should offer onabotulinumtoxinA (Level B recommendation) when efficacy is the priority, when tolerability is a concern, and when long-term or unknown harms of other medications are also a concern. The recommendation is based on high or moderate confidence in the evidence of efficacy. OnabotulinumtoxinA appears alongside certain CGRP monoclonal antibodies, topiramate, and valproate in the chronic-migraine lists. It is not listed among preferred options for episodic migraine (fewer than 15 headache days per month).

The guideline also notes that onabotulinumtoxinA may be considered for patients with medication-overuse headache and that, if a preventive is judged necessary during pregnancy for chronic migraine, it may be offered after careful risk-benefit discussion (very limited pregnancy outcome data exist, mostly from preconception or first-trimester exposures). These statements keep the recommendation tightly tied to the chronic migraine population studied in PREEMPT.

The restriction to chronic migraine is not arbitrary. The pivotal trials enrolled only patients with 15 or more headache days per month. Evidence for episodic migraine is weaker or absent for this indication, and the FDA approval remains limited to chronic migraine. Using the 155-unit protocol outside that population is off-label. Transparent counseling therefore includes both the average benefit observed in the trials and the fact that individual results vary, a substantial placebo response occurred, and many patients require ongoing treatment every 12 weeks to maintain reduced headache days.

What Patients and Clinicians Can Realistically Expect

Patients typically notice little change after the first cycle. By the second cycle (around week 24), responders often report fewer headache days, lower average severity, less acute medication use, and better ability to work, drive, or participate in family activities. Some patients experience side effects that are usually mild and temporary—neck pain, eyelid droop, or injection-site discomfort. Systemic adverse events are uncommon at the doses used for chronic migraine. The treatment does not stop a migraine already in progress; it is preventive.

Clinicians who follow the evidence therefore document baseline headache-day frequency with a diary, confirm the chronic migraine diagnosis, discuss the 24-week assessment window, and set expectations that the goal is meaningful reduction rather than elimination of headaches. When those conditions are met, the protocol aligns with both the original trial design and current guideline recommendations.

Bioethical Alignment in Practice

Beneficence is served when the 155-unit, 31-site protocol is offered only after establishing a diagnosis of chronic migraine and informing the patient of the magnitude of benefit shown in PREEMPT. Non-maleficence is served by avoiding off-label use in purely episodic migraine and by monitoring for side effects while limiting unnecessary systemic medication burden. Autonomy is served by clearly discussing the expected average reductions, the need for two full cycles before judging response, the option to continue treatment, and the availability of alternative preventive options. Patients leave the conversation able to decide whether the evidence matches their priorities.

At Injury Medical Clinic PA in El Paso, Texas, this evidence-based approach is delivered under the medical direction of Dr. Maria Guadalupe Cardenas, MD, Board Certified in Internal Medicine with more than 40 years of experience. Dr. Alex Jimenez, DC, APRN, FNP-BC, CFMP, IFMCP, a dual-licensed chiropractor and board-certified family nurse practitioner specializing in soft-tissue injury, coordinates structural and functional care alongside the medical director. The clinic is the only integrated practice in El Paso that combines these credentials with guideline-directed onabotulinumtoxinA for chronic migraine and complementary non-pharmacologic options. Patients and referring clinicians can review related educational material on migraine management and the broader standards of clinical documentation at https://dralexjimenez.com/migraine-treatment/ and https://dralexjimenez.com/trigger-point-injections-managing-myofascial-pain-effectively/.

Evidence-based protocols are anchored in the broader clinical documentation standards at https://dralexjimenez.com. When chronic migraine follows trauma, accurate headache diaries, timed clinical notes, and clear linkage of the treatment plan to the established diagnosis help both the patient and any treating or reviewing clinician understand why the intervention was chosen and how response was measured.

If you are a clinician seeking a collaborative partner for patients with chronic migraine or a patient who wants the PREEMPT protocol delivered with transparent discussion of the evidence, contact Injury Medical Clinic PA in El Paso to review whether the current AAN/AHS recommendations fit your situation.

References

Dodick, D. W., Turkel, C. C., DeGryse, R. E., Aurora, S. K., Silberstein, S. D., Lipton, R. B., Diener, H.-C., Brin, M. F., & PREEMPT Chronic Migraine Study Group. (2010). OnabotulinumtoxinA for treatment of chronic migraine: Pooled results from the double-blind, randomized, placebo-controlled phases of the PREEMPT clinical program. Headache, 50(6), 921–936.

Blumenfeld, A. M., Silberstein, S. D., Dodick, D. W., Aurora, S. K., Brin, M. F., & Binder, W. J. (2017). Insights into the functional anatomy behind the PREEMPT injection paradigm: Guidance on achieving optimal outcomes. Headache, 57(5), 766–777.

Potrebic, S., Tanveer, S., Becker, W. J., Burch, R., Cooke, L. J., Fenton, T., Fletcher, J. J., Gordon Perue, G. L., Hershey, A. D., Jackson, J. L., Kessel, S., Loder, E. W., Minen, M. T., Oskoui, M., Ramanan, V. K., Murren, M., Schwedt, T. J., Silberstein, S. D., Smith, D. B., … Pringsheim, T. (2026). Pharmacologic treatment for migraine prevention in adults practice guideline recommendations: Report of the AAN Guidelines Subcommittee and the American Headache Society. Neurology, 107(7), e214881.

American Academy of Neurology & American Headache Society. (2026). Pharmacologic treatment for migraine prevention in adults [Practice guideline]. https://www.aan.com/Guidelines/Home/GuidelineDetail/1158