How Long Does Botox Take to Work and How Long Does It Last?

How long Botox takes to work: comparing the label and hospital information

The Botox Cosmetic label says the injected muscles start to weaken 1 to 2 days after injection, getting stronger over the first week, while Siriraj and UF Health say the full effect comes at about 1 to 2 weeks. [1][4][5] In its section on frown lines between the eyebrows, the label says the injected muscles typically begin to weaken 1 to 2 days after injection and grow stronger during the first week. [1]

Siriraj Hospital in Bangkok says the drug starts to work within 2 to 3 days and reaches its peak effect in 1 to 2 weeks. [4] UF Health says Botox takes effect 7 to 10 days after injection, with the best result at 2 weeks. [5]

A systematic review of 42 studies of Dysport, a different brand of the same kind of drug, found that all 24 studies measuring within 1 week saw some response at the first time point. The most commonly reported onset was 2 to 3 days, and the earliest was 24 hours. [3] That figure belongs to Dysport, not to other brands.

The table below compares what each source wrote. Use it to see the overall range, not as a promise of which day you will see a result. From the sources we read, the most that can be said is that an effect can start from about 1 to 10 days and is strongest at about 1 to 2 weeks.

How long Botox lasts: figures from the label, pooled data and a review

The Botox Cosmetic label says the effect on frown lines between the eyebrows lasts about 3 to 4 months, and pooled trial data found a median of 120 days. [1][2] In the trials the label cites, the severity of frown lines stayed lower than with placebo for up to 120 days. [1]

A pooled analysis of four phase III trials included 621 people who received Botox. Of them, 523 (84.2%) were responders by the day-30 criteria. In that group the median duration of effect was 120 days measured at maximum frown and 131 days measured at rest. [2] That median covers only people who responded at day 30, not everyone, and it means that half of that group lasted longer and half shorter. [2] The authors concluded that more than half of responders had a sustained benefit for 4 months. [2]

Siriraj says the effect lasts 3 to 4 months, after which the muscles gradually return to moving as before. [4] UF Health says results last up to 4 months. [5]

The Dysport review reported duration most often as 4 months (18 studies), with 4 studies showing the effect still present at 5 months and 3 at 6 months or longer; all 37 studies that assessed duration showed some response after 12 weeks. [3] The authors summarised the range as 3 to 6 months. [3]

Different areas and uses give different figures. The BOTOX label reports a median duration of response of 201 days in its studies for severe underarm sweating. [6] So the frown line figure should not be applied to every area.

Why the timing figures for Botox differ between sources

Each source measures in a different way, for a different brand and a different area, so they cannot be compared directly, and no figure predicts your own result in advance. [3][2][6] The Dysport review itself says the studies used different methods to measure onset and duration. [3]

The Botox label measures at day 30, with the investigator rating frown line severity at maximum frown and the person rating their own change. [1] The pooled analysis used a doctor's wrinkle scale plus the person's own rating and calculated medians with the Kaplan-Meier method. [2] The UF Health page and the Siriraj leaflet are patient information and do not state how the figures were measured. [4][5]

The pooled analysis also found that people who rated their own improvement higher at day 30 tended to have a longer effect on lines at maximum frown, but no such link was found for lines at rest. [2]

The figures above come from the BOTOX Cosmetic label, pooled BOTOX data and a review of Dysport. We found no comparison between the brands sold in Thailand in the sources we read. Other brands have their own labels, so ask your doctor what data exist for the brand used, and check the current registration status with the Thai FDA (อย.). For the names and types of botulinum toxin, see [[botox-botulinum-names]].

Ask your doctor when the result will be assessed, and take photos from the same angle both at rest and while frowning so you can compare, instead of checking the mirror every day.

If you see no result, or it wears off early: what to do

We found no standard rule for how many days is too long, so go to your follow-up and tell the doctor who injected you if the result is not what you expected. [4][1] Siriraj advises attending the follow-up visit so the result can be assessed, and telling the doctor about anything abnormal. [4]

Siriraj writes that the effect of Botox is not permanent, so treatment must be repeated to maintain it, and that long-term use can lead the body to form antibodies, which can shorten the effect. [4] How often to repeat is left to the doctor by the label, so this article gives no figure. [1]

The label asks you to tell your doctor which botulinum toxin products you have had before and to make sure the doctor knows exactly which product you received. [1] Keep a note of the brand each time.

What to expect while Botox is taking effect, and when to get urgent help

Side effects usually appear within the first week and many clear by themselves, but trouble swallowing, speaking or breathing needs urgent medical contact. [1][4] The label says side effects usually occur within the first week after injection; many are temporary, but some can last several months or longer. [1]

Siriraj reports that side effects such as headache, bruising, drooping eyelid or brow and local muscle weakness are usually mild to moderate and clear by themselves in 1 to 2 weeks. [4]

The Botox patient information says swallowing, speaking and breathing problems can occur from hours to weeks after injection, and to call your doctor or get medical help right away. [1] For the full aftercare advice and warning signs, see [[botox-aftercare-dos-donts]].

• Trouble swallowing, speaking or breathing [1]
• Weakness all over the body, double or blurred vision, hoarse voice [1]
• Rash, itching, wheezing, dizziness or fainting, which are allergic reactions [1]