Headache After Botox: Why It Happens and How Long It Lasts
Reviewed for medical accuracy against our Medical Review Board · Last updated 24 August 2026
Part of Botox Guides: Basics, Dosing and Safety
Yes, Botox can cause a headache, and the label puts a number on it: 9 percent of people treated for forehead lines reported one, which makes it the most common adverse reaction of that treatment. The number worth knowing alongside it is the placebo figure, 5 percent. Roughly half of the headaches that follow a Botox appointment would have happened anyway.
If you are reading this a day or two after an appointment, the short version is that an ordinary post-injection headache starts within the first week, is dull rather than severe, and fades over days without treatment. The section on when it is not ordinary is the one to read if yours is severe, getting worse, or came with anything happening to your swallowing or breathing.
1. How common it actually is
BOTOX Cosmetic's label summarises the most common adverse reaction for each treated area, and for one area that reaction is a headache:
| Area treated | Most common adverse reaction |
|---|---|
| Frown lines, glabella | Eyelid drooping, 3% |
| Crow's feet, lateral canthal lines | Eyelid swelling, 1% |
| Forehead lines, with frown lines | Headache, 9%, and brow drooping, 2% |
Nine percent is roughly one person in eleven. That is common enough that an injector treating a full appointment book sees it every week, and it is the single most likely unwanted effect of having your forehead done.
2. It depends which area you treated
This is the part that is almost never said, and it is the most useful thing on this page. Headache does not appear as a reported reaction in the trials of every area. It appears in the forehead trials and not in the others.
| Trial | Treated | Reactions reported at 1% or more |
|---|---|---|
| Frown lines only | 405 | Eyelid drooping 3%, facial pain 1%, facial weakness 1%, muscle weakness 1% |
| Crow's feet only | 526 | Eyelid swelling 1% |
| Forehead plus frown lines | 665 | Headache 9%, eyelid drooping 2%, brow drooping 2%, skin tightness 2% |
Read the first two rows again. In 405 people treated for frown lines alone and 526 treated for crow's feet alone, headache never reached the one percent reporting threshold. It shows up only where the frontalis, the broad sheet of muscle across your forehead, was injected.
What that means for you. If you had your forehead treated and you have a headache, you have the single most commonly reported effect of that specific treatment, and it is expected. If you had only your frown lines or only your crow's feet done, a headache is less clearly connected to the injection, and coincidence deserves more weight.
One honest caveat about reading those tables. A reaction missing from a table does not mean it never happened. The threshold is "at least 1 percent and more often than placebo", so a reaction at 0.8 percent, or one that happened just as often in the placebo group, would not be listed. The tables show where the signal was strong enough to attribute, not the total of everything anyone experienced.
3. Can Botox cause headaches, or is it coincidence?
Both, and the trials separate the two for you. In the forehead studies, 58 of 665 treated subjects reported a headache, which is the 9 percent figure. In the same studies, 17 of 315 subjects who were injected with saline also reported one, which is 5 percent.
| Group | Reported a headache | Rate |
|---|---|---|
| BOTOX Cosmetic, 20 units forehead with 20 units glabellar | 58 of 665 | 9% |
| Placebo, saline injections | 17 of 315 | 5% |
| Difference attributable to the drug | about 4 points |
So the answer is not a simple yes. Botox does cause headaches, at a rate of roughly one in 25 above what would have happened regardless. But 5 percent of people got a headache from being injected with salt water, which tells you how much of this is the appointment rather than the drug: the needles, the tensing, the held-still posture, the anxiety, and the ordinary background rate of headaches in adults on any given day.
If you are deciding whether to book, that is the honest framing. Not "Botox gives you headaches", and not "headaches are unrelated". About one person in eleven will have one, and about half of those would have had one anyway.
4. Why it happens
There is no single accepted mechanism, and any article that gives you one confident explanation is overstating what is known. Several things are plausible and more than one can be true at once:
- The muscle is learning a new job. The frontalis lifts your brows. Partly weakening it changes the balance between it and the muscles that pull the brows down, which keep working normally. The recruitment pattern while that settles is a reasonable candidate for a dull ache across the forehead and temples.
- Brow heaviness reads as head pain. If the frontalis is over-treated, the brows sit lower and the muscles around the eyes work harder to compensate. People often describe that as pressure or a headache rather than as a heavy brow. It is the same problem discussed on our droopy eyelid after Botox page, and the label lists brow drooping at 2 percent in these same trials.
- The injection itself. Needles into the periosteum-adjacent tissue of the forehead hurt, and post-needle head pain is well recognised with any injection there.
- Tensing and position. Holding still, frowning on command, and clenching through an injection are all headache triggers in people who are prone to them.
What it is almost certainly not is the toxin reaching your brain. Botulinum toxin injected into facial muscle acts locally at the neuromuscular junction, and the systemic effects the label does warn about are muscle weakness and swallowing and breathing problems, not head pain.
5. The dose paradox, and the migraine contradiction
Here is the thing that confuses people most, and it is a fair confusion: Botox is an FDA approved preventive treatment for chronic migraine, and it also causes headaches. Both are true.
The doses make it stranger. A cosmetic forehead and frown line treatment is about 40 units. The chronic migraine protocol is 155 units across 31 sites, and the trials used up to 195. Four to five times the dose, and yet:
| Setting | Dose | Headache, treated | Headache, placebo |
|---|---|---|---|
| Cosmetic, forehead with frown lines | 40 units | 9% | 5% |
| Chronic migraine prophylaxis | 155 to 195 units | 5% | 3% |
More units, lower reported rate. Be careful what you conclude from that, because these are not comparable populations: everyone in the migraine trials already had at least 15 headache days a month, so a new headache is far harder to notice and to attribute. The comparison does not prove that bigger doses are gentler. What it does dispose of is the common assumption that headache after Botox is a dose problem, or a sign you were given too much. The evidence does not support that reading.
The reconciliation is that dose is not the variable that matters most here. Where the injections go, what those muscles do, and why you were injected in the first place matter more.
6. When it starts and how long it lasts
The label is general rather than specific on timing, and what it says is that adverse reactions "occur within the first week following injection" and are generally transient. Applied to headache, and consistent with what injectors report:
- Onset: usually the same day or the day after, and within the first week.
- Duration: most resolve within a few days. This is not a headache that tracks the three to four month life of the treatment.
- The exception: if it is brow heaviness being felt as pressure, it can persist for weeks, because it lasts as long as the muscle weakness does rather than as long as the injection soreness.
A headache that starts three weeks after an appointment is unlikely to be the injection. A headache that starts the same evening probably is.
7. What actually helps
- Ordinary painkillers. Paracetamol or acetaminophen is the usual first choice. Some clinics prefer you avoid ibuprofen and aspirin for a day or two after injection because they thin the blood slightly and can worsen bruising, so if bruising matters to you, use the other one. This is a bruising precaution, not a safety rule about the toxin.
- Water and food. Underhydration and a skipped meal before an appointment are headache triggers in their own right, and appointments are often squeezed into a lunch break.
- Time. For most people this is the entire answer, and it is unsatisfying but true.
- Telling the clinic. Worth doing even if it resolves, because it belongs in your notes and it should change the plan next time. There is no reversal agent for botulinum toxin, so nothing can be undone; the value of reporting it is the record, not a fix.
8. When it is not ordinary
Two thresholds are worth knowing, and one of them is a real number rather than a vague caution.
The first comes from the chronic migraine trials. Severe worsening of migraine, bad enough to require hospital admission, occurred in about 1 percent of treated patients against 0.3 percent on placebo, usually within the first week after treatment. That is uncommon, and it was recorded in patients receiving the much larger therapeutic dose, but it establishes that a severe worsening after injection is a documented outcome rather than something that cannot happen.
The second is the boxed warning, which is on every botulinum toxin product sold. It is not about headache, and that is exactly why it is useful here: it tells you which symptoms are a different category of problem. Seek medical help promptly for any of these, whether or not a headache came with them:
- Difficulty swallowing, or a sense that food or liquid is going down wrong
- Difficulty breathing, or shortness of breath
- Slurred speech or a change in your voice
- Double vision or a drooping lid that appeared suddenly with other symptoms
- Generalised muscle weakness, or weakness away from the injected area
- Loss of bladder control
The label notes these have been reported hours to weeks after injection, and that swallowing and breathing difficulties can be life threatening. Alongside those, treat a severe headache that is getting worse rather than better, a headache with fever and neck stiffness, or the worst headache of your life, as reasons to be seen the same day. None of those are typical of a post-injection headache.
9. What to change next time
A headache once does not mean you cannot have Botox again. It means there are things worth raising before the next appointment:
- Ask about the forehead dose specifically. The evidence points at the frontalis, and that is the area where dose and placement are most often the difference between a good result and a heavy brow. Our units guide sets out typical ranges, and the forehead article covers why treating it without the frown lines is the classic setup for trouble.
- Say it happened, and when. Same day, day after, or a week later changes the interpretation.
- Say whether your brows felt heavy. This is the question that separates a short-lived injection headache from weeks of compensating for an over-treated forehead, and it changes what should be done differently.
- Mention your own headache history. If you get migraines already, that belongs on the record before treatment, not after.
- Check who is injecting. Placement in the frontalis is anatomy-dependent and the consequences of getting it wrong show up as brow heaviness. Our guide on verifying an injector's licence covers how to check.
And if you came here because you are weighing up a first appointment: this is a common, mild, short-lived effect with a real but modest attributable rate. It is worth knowing about. It is not, on these numbers, a reason not to go.
Frequently asked questions
Can Botox cause headaches?
How long does a headache after Botox last?
Is a headache after Botox normal?
Why does Botox treat migraines but also cause headaches?
Does a headache mean I had too much Botox?
What can I take for a headache after Botox?
When should I worry about a headache after Botox?
Can Botox make existing migraines worse?
Know the count before the quote. The unit count is half the bill, and a low per-unit rate recovered by a high unit count is the commonest way a deal is not one. How to tell.
Deciding which area, not how many units? Botox by facial area covers what each zone actually achieves, which four are FDA approved, and the things Botox cannot fix at all.
