The standard Botox treatment for chronic migraines uses 155 units, split across 31 injection sites in seven muscle areas of the head and neck. This is known as the PREEMPT protocol, and it’s the only FDA-approved approach for administering Botox for migraine prevention. Each injection site receives 5 units.
How the 155 Units Are Distributed
The 155 units aren’t concentrated in one spot. They’re spread deliberately across seven muscle groups, with some areas receiving significantly more than others. Here’s the full breakdown:
- Temporalis (temples): 40 units across 8 sites, the largest share
- Occipitalis (back of the head): 30 units across 6 sites
- Trapezius (upper shoulders/neck): 30 units across 6 sites
- Frontalis (forehead): 20 units across 4 sites
- Cervical paraspinal group (back of the neck): 20 units across 4 sites
- Corrugator (between the eyebrows): 10 units across 2 sites
- Procerus (bridge of the nose): 5 units in 1 site
The temples and the back of the head get the heaviest dosing because these are the muscle groups most involved in chronic migraine pain patterns. The protocol uses fixed sites and fixed doses, meaning your provider follows the same map every session rather than customizing placement. This standardized approach is what was tested in the clinical trials that led to FDA approval.
Who Qualifies for Treatment
Botox is FDA-approved specifically for chronic migraine, defined as 15 or more headache days per month, with headaches lasting four hours or longer per day. It is not approved for episodic migraine, which is 14 headache days or fewer per month. The FDA label states directly that safety and effectiveness have not been established for episodic migraine.
If you have chronic migraine and want insurance to cover the treatment, most plans require you to have tried and failed preventive medications from at least two or three different drug classes first. These typically include a beta-blocker, an antidepressant commonly used for migraine prevention, and an anti-seizure medication. The specific requirements vary by insurer, but the pattern is consistent: Botox is generally treated as a second- or third-line option, not a first choice.
Treatment Schedule and What to Expect
Treatments are given every 12 weeks (roughly every three months). The procedure itself takes about 15 to 20 minutes. Your provider uses a very fine needle to deliver 31 small injections, each containing just 0.1 mL of fluid. Most people describe the sensation as a brief pinch at each site.
Botox for migraines doesn’t work immediately. Many patients don’t notice significant relief until after their second or third round of treatment, meaning it can take six to nine months to see the full benefit. This delayed response is one of the most common reasons people give up on the treatment too early. If your provider recommends sticking with it through at least two or three cycles before deciding it isn’t working, that’s standard guidance based on how the clinical trials were designed.
Common Side Effects
The most frequently reported side effect is neck pain and stiffness, which typically shows up in the week after treatment. This happens because surrounding muscles compensate for the ones that have been temporarily relaxed by the injections. It usually resolves on its own within a few days.
Other possible side effects include mild pain or bruising at injection sites, a headache on the day of or day after the procedure, and temporary cosmetic changes like reduced forehead wrinkles or a slight shift in eyebrow shape. Less commonly, patients experience a temporary drooping of one eyelid. Rarely, some people develop flu-like symptoms (muscle aches, fever, fatigue) that last a few days and typically don’t recur with future treatments.
Why the Dose Stays at 155 Units
Unlike cosmetic Botox, where doses are tailored to individual goals, the migraine protocol is standardized. The 155-unit, 31-site approach was the exact regimen tested in the large clinical trials (called PREEMPT 1 and PREEMPT 2) that proved Botox works for chronic migraine. Straying from that protocol means moving outside the evidence base.
Some providers do add extra units to specific areas if a patient has a particularly stubborn pain pattern, but the core protocol remains 155 units. If you’re quoted a dramatically different number, it’s worth asking how the dosing plan compares to the standard PREEMPT protocol and why.