How Often Should Botulinum Toxin Be Repeated? — Duration and Interval
The figure for a single session is not what decides the whole of it — how many months apart is. Four months or six months changes how many treatments a year contains. And a shorter interval is not simply better: there is a problem that belongs specifically to short intervals. This column collects the data by area, with its limits.
The short answer
Duration differs by area and by dose design, and we take a minimum of three months before treating the same area again. The US label states a duration of approximately 3–4 months and that treatment more frequently than every three months has not been clinically evaluated. In masseter data, thickness fell at one month, was held to three months and was similar to the untreated arm by six months. With a short interval, neutralising antibodies can rarely reduce the effect, and short dosing intervals and a high dose per session are cited as contributing factors. Miso Clinic in Daegu (4F Bombom Building, 125 Dongdeok-ro, Jung-gu, Daegu, South Korea; +82-53-428-2700) reviews the result at two weeks and keeps same-area treatment at least three months apart.
Duration differs by area
“Three to six months” is the usual shorthand, and the label itself says approximately 3–4 months. Inside that range, though, the area, the dose and which measure you read move the answer.
Muscle thickness on ultrasound, what the patient notices, and a machine measurement do not disappear at the same time. The data below is read with the measure attached.
Onset and the approved dose for each area are collected separately in onset, duration and approved doses. This column stays on the second half: how long it holds, and when the next one goes in.
Masseter — down at one month, held to three, back near baseline at six
- 1 monthThickness fallsIn a randomised ultrasound study of 48 patients with bruxism, thickness fell in the toxin arm.
- 3 monthsHeldThe reduction was maintained to three months in the same study.
- 6 monthsSimilar to untreatedBy six months it was similar to the untreated arm. It comes back.
A separate prospective cohort of 8 patients measured the curve directly: greatest reduction at week 11 (31.1% on clenching · 25.8% at rest, p<0.05), week 15 28.8%/24.6%, week 25 20.1%/15.6% with significance lost. The sample is very small.
Trials using prominence as the measure took day 90 as the main assessment point, and the dose-ranging trial allowed re-injection at day 180 if needed. Read together, a single masseter treatment sits in a three-to-six-month frame — although the meta-analysis concluded that the optimal dose and schedule are not established.
Skin botox — each measure faded at a different time
- Double-blind split-face study of 18 people in the cheek — pores improved at week 2 only, texture at week 8, nasolabial wrinkles to week 12. Sebum production and under-eye wrinkles showed no significant difference.
- Multicentre randomised double-blind study of 49 people in the scalp — sebum significantly lower at 1 and 3 months, no difference at 4 and 6 months. Scalp data, not facial.
- Randomised double-blind study of 42 women in the forehead — sebum at the injection points returned to baseline by week 16.
So a single duration for skin botox is hard to state. What you are hoping for changes what duration means. Pores point to weeks, texture to a couple of months, sebum to data that splits.
For the glabellar area, measured medians exist: 140.65 days in women and 116.61 days in men, with sex the main predictor. Full effect ran 44 to 56 days and partial effect 99 to 145 days in a contralateral-control study.
What goes wrong when the interval is short
“Can I come back as soon as it starts to fade?” is a frequent question. Two things are worth knowing.
First, rarely, neutralising antibodies can reduce or abolish the effect. The factors cited are short dosing intervals (booster injections), a high dose per session, and a high antigenic protein load. A short interval is exactly one of those factors. The label also states that treatment more frequently than every three months has not been clinically evaluated, with a cumulative ceiling of 360 Units per three months.
Second, a greater reduction can come with more functional change. In 26 women randomised to a second injection or saline three months after the first, the second-injection arm had a greater reduction in thickness at six months but also greater change in masseter electromyography, temporalis thickness and painful sites.
So we keep the same area at a minimum of three months, and when the result feels short we look again at the point design rather than at the calendar.
Why we review at two weeks
Toxin does not act at the moment of injection; the effect rises over days to about two weeks. So a review at two weeks is part of the design rather than an optional extra.
At that visit we add where it is short and balance the two sides. Putting in a generous dose at the start cannot be undone — it can only be waited out. Measured against the standard that a good treatment should not be conspicuous, starting short and correcting at two weeks is the better order.
Does repeating it leave changes in bone or muscle?
This comes up constantly with the masseter. Two pieces of data.
- A systematic review and meta-analysis found about a 6% reduction in cortical bone thickness in humans, with no clear change in volume or density — and noted that repeated or high-dose use has barely been studied.
- A CT study of 123 patients found no meaningful change in bone density with one to two treatments over a year (authors include manufacturer employees).
In other words, no clear change is reported in the usual range of treatments, and there is no data for heavy repetition. That gap is another reason to lengthen rather than shorten the interval.
Sessions decide what the whole thing adds up to
Comparing a single figure misses the shape of it. How many treatments a year contains matters more, and that number comes from the area and its duration.
The questions worth asking are these: which area and how many points, is the two-week review included, and what decides the next session. A fee means something only after the design is fixed.
Summary — established and not established
Established
- Masseter thickness fell at one month, held to three months and was similar to the untreated arm at six months (48 patients, ultrasound).
- The US label states duration of approximately 3–4 months and that more frequent treatment than every three months has not been clinically evaluated.
- Skin botox measures faded at different times (pores week 2 · texture week 8 · nasolabial week 12).
- Short dosing intervals, high dose per session and high antigenic protein load are cited as contributing factors for neutralising antibodies.
- A second injection at three months gave a greater reduction in thickness at six months but greater functional change (26 women).
Not established
- The optimal dose and schedule for the masseter — the meta-analysis concluded they are not established.
- Changes in bone or muscle after years of repetition — repeated and high-dose use is barely studied.
- The interval at which skin botox should be repeated — we found no human comparison of intervals.
- Why duration differs between individuals — apart from sex in the glabellar data, predictors are not established.
Botulinum toxin duration: frequently asked questions
How often should masseter botulinum toxin be repeated?
In the data, the reduction in thickness held to three months and was similar to untreated by six months. We keep the same area at a minimum of three months and decide the next session from the result.
It is fading. Can I have it again straight away?
We would not advise it. Rarely, neutralising antibodies can reduce the effect, and short dosing intervals and a high dose per session are cited as contributing factors. The label also notes that more frequent treatment than every three months has not been clinically evaluated.
How long does skin botox last?
It depends on the measure you are hoping for. In an 18-person cheek study, pores improved at week 2 only, texture at week 8 and nasolabial wrinkles to week 12, while sebum showed no significant difference.
Does long-term use weaken the jawbone?
A meta-analysis found about a 6% reduction in cortical bone thickness, and a CT study of 123 patients found no meaningful change in bone density with one to two treatments over a year. There is almost no data on heavy repetition.
Do I really need to come back at two weeks?
The effect rises over about two weeks, so that is when we add where it is short and balance the sides. A generous first dose cannot be undone, so we start short and correct at the review.
Read next
Product pages
No separate English product page yet — the approved doses, the label wording and the adverse-event rates for botulinum toxin are collected in our onset and duration column.
Who wrote this
Written and reviewed by Lee Chi-Hak, MD, director of Miso Clinic, Daegu. The treatment standards and injection design set out here are the ones we use in practice.
| Medical director | Lee Chi-Hak, MD |
|---|---|
| Address | 4F Bombom Building, 125 Dongdeok-ro, Jung-gu, Daegu, South Korea · Exit 1, Kyungpook National University Hospital Station |
| Phone | +82-53-428-2700 |
| Hours | Weekdays 11:00–19:00 (lunch 13:00–14:00) / Saturday 10:00–16:00 (no lunch break) / Closed Sundays and public holidays |
| Columns | All clinical columns |
| Reference library | All booster and device references |
References
- Miso Clinic botulinum toxin notes — a Unit is biological potency, not a volume, and because potency assays differ between manufacturers, Units do not convert 1:1 between products. Target muscle by area, dose and point design, a check at two weeks, and a minimum of three months between treatments of the same area.
- US FDA prescribing information (BOTOX Cosmetic, onabotulinumtoxinA, revised October 2024) — onset “one to two days after injection, increasing in intensity during the first week”, duration “approximately 3-4 months”, re-treatment “more frequently than every 3 months have not been clinically evaluated”, cumulative ceiling 360 Units / 3 months.
- Masseter thickness in bruxism, randomised — Taşdemir E et al., J Oral Maxillofac Surg 2025;83(12):1453–1460, PMID 40935351. 48 patients, ultrasound. Thickness in the toxin arm fell at one month and was maintained to three months, but by six months it was similar to the untreated arm.
- The masseter time curve — Lee et al., Archives of Aesthetic Plastic Surgery 2016 — prospective cohort of 8 patients (8 at week 15 · 4 at week 25), 32 to 40 Units per masseter. Greatest reduction at week 11 (31.1% on clenching · 25.8% at rest, p<0.05), week 15 28.8%/24.6%, week 25 20.1%/15.6% (significance lost at p=0.125). The sample is very small.
- Masseter prominence, phase 2b — Liew S et al., Aesthet Surg J 2025;45(10):1043–1050, PMID 40111171. 48 Units in 53 patients · 72 Units in 46 · placebo in 46, single treatment. At day 90, prominence of grade 3 or less was reached by 90.6% and 91.3% against 21.7% for placebo. Authors include manufacturer (Allergan) employees.
- Masseter prominence, phase 2 (24–96 Units) — Carruthers J et al., J Am Acad Dermatol 2025;92(3):464–472, PMID 39522729. 187 patients, re-injection at day 180 if needed. Lower-face volume and prominence fell against placebo, there was no clinical change in jawbone or teeth, and 4 patients in the 96-Unit arm reported a local effect on smiling. Authors include manufacturer employees.
- Meta-analysis in masseteric hypertrophy — Machado GF et al., J Plast Reconstr Aesthet Surg 2026;119:212–225, PMID 42379083. Five placebo-controlled randomised trials, 536 patients. Thickness, prominence and satisfaction improved against placebo, but heterogeneity was high, so the size of the reduction should be read with care, and the review concluded that the optimal dose and schedule are not established.
- Intradermal toxin in the cheek, double-blind split-face — Shin DM et al., Ann Dermatol 2022;34(6):442–450, PMID 36478426. 18 subjects, incobotulinumtoxinA in one cheek and saline in the other. No significant difference in sebum production or under-eye wrinkles; pores improved at week 2 only, texture at week 8 and nasolabial wrinkles to week 12. One subject who received 30 Units in one cheek reported facial palsy; there were no adverse events at 20 Units.
- Intradermal toxin in the scalp, multicentre randomised double-blind — Li Y et al., Aesthet Surg J 2023;43(1):NP38–NP48, PMID 36004504. 49 subjects (25 toxin · 24 saline), one session of 50–65 Units. Sebum was significantly lower at 1 and 3 months and no different at 4 and 6 months. This is scalp data, not facial data.
- Sebum by distance after intramuscular forehead injection — Min P et al., Aesthet Surg J 2015;35(5):600–610, PMID 25825422. 42 women, 10 Units against 20 Units, randomised and double-blind. Sebum fell at the injection points but rose beyond a 2.5 cm radius at weeks 2, 4 and 8; 4 Units per point was neither stronger nor longer-lasting than 2 Units, and values returned to baseline by week 16.
- Measured onset and duration — Rappl T et al., Clin Cosmet Investig Dermatol 2013;6:211–219. Randomised, double-blind, 180 patients (179 analysed). For onabotulinumtoxinA, median time to onset 5.29 days in women · 5.89 days in men; median duration 140.65 days in women · 116.61 days in men, with sex the main predictor of duration.
- Full effect against partial effect — Nestor MS & Ablon GR, J Clin Aesthet Dermatol 2011. Randomised, double-blind, contralateral frontalis control, 20 patients (40 sides). For onabotulinumtoxinA, full effect 44 to 56 days and partial effect 99 to 145 days.
- Antibodies and loss of effect — Bellows S, Jankovic J, Toxins 2019;11(9):491, PMID 31454941. Rarely, neutralising antibodies can reduce or abolish the effect; short dosing intervals (booster injections), high dose per session and a high antigenic protein load are cited as contributing factors.
- A second injection at three months — de Souza Nobre BB et al., Sci Rep 2024;14:14522, PMID 38914688, and the same group, Aesthetic Plast Surg 2024;48(19):3979–3987, PMID 38740627. 26 women randomised to toxin or saline three months after the first treatment. The second-injection arm had a greater reduction in thickness at six months but also greater functional change in masseter electromyography, temporalis thickness and painful sites.
- Effect on bone — Moussa MS et al., J Oral Rehabil 2024;51(2):404–415, PMID 37668276 (systematic review and meta-analysis: about 6% reduction in cortical bone thickness in humans, no clear change in volume or density, and repeated or high-dose use barely studied) · Kostenuik P et al., Aesthet Surg J 2026;46(1):76–85, PMID 40843518 (123 patients, CT; no meaningful change in bone density with one to two treatments over a year; authors include manufacturer employees).
- Medical advertising law — Medical Service Act of Korea, Article 56(2), which prohibits testimonial advertising, comparison with other clinics, superlative claims and advertising that guarantees or implies a guaranteed treatment effect.
- Miso Clinic practice guidance — indication criteria, site-by-site design, and the explanation and consent procedure. This is the source for every sentence marked as clinical judgement.
Everything in this column is general information and does not replace medical diagnosis or treatment. Effects and side effects vary with individual skin condition, age and underlying illness, and the same result is not guaranteed for everyone. Any decision to proceed should be made in an in-person consultation with a physician.