How long does Botox take to work?

How long the toxin takes to work is often the first question people ask before an injection, especially when a date is coming up. It is one of the basics covered on our page on botulinum toxin explained for patients. The answer depends on the family of toxin used, and two quite different moments need to be distinguished: when first effects appear, and when the effect peaks.

First effects and peak effect: two different moments

First effects are the moment when you start to feel or see that the muscle contracts less: the frown is a little weaker, the line deepens a little less. The peak effect is when this relaxation reaches its strongest level. The effect then holds for a while, before gradually decreasing.

Between these two moments, the effect builds day by day. This is why a result judged too early can look insufficient, or uneven from one side to the other, when it is simply still settling in. This gap is the source of a lot of needless worry in the first few days.

Why doesn’t the toxin work immediately?

Botulinum toxin does not simply sit in the muscle. It must first bind to the nerve endings, enter them, then release its active part, which cuts a protein needed to release acetylcholine, the messenger of contraction^2,4,8. Each of these steps takes time, and the blockade builds up gradually². The mechanism is explained in detail on our page on how botulinum toxin acts on the muscle.

The time it takes for effects to appear is not the same for both families of toxin: this is one of the differences between type A toxins and the short-acting botulinum toxin (serotype E), as their labels show^2,4.

How long does the long-acting toxin take to work?

For type A toxins approved for aesthetic use, the labels give similar timings:

• the median time to first effects is 2–3 days^1,6;
• some patients report an effect within 24 hours⁷;
• one label states that the effect generally appears within a week², another that improvement begins during the week following the injection³.

The peak effect comes later. Depending on the product, it is seen during week 2³ or around day 30^1,6. The pharmacology section of one label even places the peak 5–6 weeks after the injection². To keep it simple, remember "peak effect between week 2 and week 4", knowing that it may come a little later depending on the product².

And the short-acting botulinum toxin?

It works faster. Its label states that "the clinical effects begin to manifest 8 hours post-injection"⁴. This figure is the first time point measured in the trials: it is the start of the effect, not a complete effect. The peak effect is seen around day 7⁴.

The trials give an idea of how the effect builds. In the phase 2b trial, at the highest dose, 16.1% of patients responded to treatment at 8 hours, 41.9% at 24 hours and 93.3% at day 7⁵. In other words, the effect is visible in some patients from the first day, but it keeps building throughout the first week. This trial was funded by the manufacturer⁵.

Approval of this toxin depends on the country. As of 9 October 2026, it is approved in the European Union (since 15 July 2026) and in Canada (since 22 June 2026), for frown lines only^9,10.

Comparing onset times

For a type A toxin: first effects usually within 2–3 days (up to one week), peak effect between week 2 and week 4^1,2,3. For the short-acting toxin: first effects from 8 hours, peak effect around day 7⁴. No trial compares the two families directly: these figures come from their respective labels.

Onset says nothing about duration, or rather it suggests the opposite: the toxin that works fastest is also the one whose effect lasts the shortest time. For that second question, see our page answering how long the toxin lasts with each family.

The result day by day: what to expect

Without claiming to describe every case, here is how the first weeks usually unfold, according to the labels:

• On the day of the injection: slight redness or mild swelling at the injection points is possible; it is caused by the needle, not by the effect of the toxin². With the short-acting toxin, first effects may begin the same day⁴.
• The first few days: with a type A toxin, first effects most often appear between day 2 and day 3^1,6.
• The first week: the short-acting toxin reaches its peak effect around day 7⁴; a type A toxin is still settling in³.
• Between week 2 and week 4: a type A toxin reaches its peak effect^1,3.

Only at this stage can the result be judged, in particular its symmetry.

When should you judge the result?

Wait for the peak effect before drawing conclusions. An asymmetry or an effect that seems too weak in the first days may still change. If, after that point, the result is not what was planned, talk to the doctor who performed the injection. One label states that if there is no improvement after the first session, the causes should be investigated⁶: dose, injection technique or, more rarely, antibodies.

Avoid asking for another injection in the days that follow: excessive muscle weakness may be made worse by another toxin injected before the effects of the previous one have worn off², and after the short-acting toxin, a type A toxin injected less than 30 days later has not been evaluated⁴.

And before an event?

These timings matter if you have a date in mind. Our page on planning botulinum toxin ahead of an event turns them into reference points for both families of toxin, without recommending one over the other. In every case, allowing some margin gives you time to judge the result and to talk to your doctor if needed.