A dose of 20 units of Botox typically lasts 3 to 4 months. This is the FDA-recommended dose for frown lines between the eyebrows (glabellar lines), split across five injection sites at 4 units each. Most people start noticing movement returning around month three, with the full effect wearing off by month four as the muscles gradually regain their ability to contract.
What 20 Units Covers
Twenty units is a precise, well-studied dose, and where it goes on your face matters. For glabellar lines (the vertical “11” lines between your brows), 20 units is the standard treatment. For horizontal forehead lines, the typical range is 10 to 20 units, so 20 units would sit at the higher end. For crow’s feet, each side usually requires 5 to 15 units, meaning 20 units could treat both sides comfortably.
If your provider splits 20 units across multiple areas rather than concentrating them in one spot, the effect in each area will be lighter, and it may not last as long. Underdosing a specific area is associated with shorter duration, lower response rates, and less patient satisfaction compared to using the full recommended dose for that zone.
When Results Start and Peak
You won’t see results the day of your appointment. Some people notice subtle changes as early as 3 to 4 days after injection, but most see visible results within 10 to 14 days. Maximum smoothing typically arrives around the two-week mark, sometimes stretching to three weeks. This is when the treated muscles are at their most relaxed and lines are at their flattest.
How the Effect Fades
Botox works by blocking nerve signals to the injected muscles, preventing them from contracting. Over time, your nerve endings essentially build new pathways to communicate with the muscle again. This process happens gradually, not all at once. You might notice small twitches or the ability to furrow your brow slightly around month two or three. By month three to four, enough nerve-muscle communication has restored that wrinkles begin forming again with facial expressions.
The fade is slow enough that most people don’t wake up one morning looking dramatically different. Lines creep back in over several weeks, which is why many providers schedule follow-up appointments at the 3- to 4-month mark to maintain a consistent look.
Why It Lasts Longer for Some People
The 3-to-4-month window is an average. Several factors push your results toward the shorter or longer end of that range.
- Metabolism and activity level: People with faster metabolisms tend to break down Botox more quickly. Frequent high-intensity exercise increases circulation and metabolic rate, which can shorten how long results last.
- Muscle strength: Stronger, thicker facial muscles may overpower a standard dose sooner. People who are very expressive or who have particularly strong frown muscles sometimes find 20 units wears off closer to the 3-month mark.
- Treatment history: Your first session may wear off faster than later ones. With repeated treatments over time, the targeted muscles weaken from lack of use, so each subsequent round of Botox can last a bit longer than the one before.
- Dose adequacy: Clinical data shows that higher doses tend to last longer. Twenty units is the standard for glabellar lines, but some providers use slightly higher doses for patients with strong muscles or those who metabolize Botox quickly. There is growing evidence that doses above the standard can improve outcomes without increasing safety risks.
First-Timers Often Need Earlier Touch-Ups
If this is your first time getting Botox, expect results to wear off sooner. Many first-time patients find themselves returning at the 2- to 3-month mark rather than waiting the full four months. This is normal. Your muscles haven’t yet started the gradual weakening process that comes with repeated treatments, so they bounce back to full strength faster. By your second or third session, you’ll likely get closer to the 4-month duration most people associate with Botox.
Maintaining Results Over Time
Consistent treatment actually works in your favor. As the muscles responsible for frown lines or forehead creases weaken from repeated Botox sessions, they produce less prominent lines even as each dose wears off. Some long-term users find they can eventually space their appointments further apart, going five or even six months between sessions, because the muscles simply aren’t as strong as they used to be.
Skipping appointments or waiting too long between sessions lets the muscles fully recover their strength, essentially resetting the clock. If maintaining smooth results matters to you, staying on a regular schedule gives you better and longer-lasting outcomes over time.