Botulinum Toxin Injection (Anal Fissure)

Overview

When you have a chronic anal fissure — a tear in the lining of your anal canal that hasn't healed after six weeks or more — the muscle beneath it, called the internal anal sphincter, tends to be locked in a state of constant, excessive tension. That tension squeezes the blood supply to the wound, which is why creams alone often don't work: the fissure simply cannot heal when it isn't getting enough circulation.

Botulinum toxin is injected directly into that sphincter muscle to temporarily relax it. The effect lasts for about 3 to 4 months — which is long enough for the fissure to heal in most people. Crucially, this approach does not involve any permanent cut to the muscle, so there is no lasting change to your bowel control. The procedure is done under a general anaesthetic or sedation as a day case, and you go home the same day.

Who needs this procedure?

A botulinum toxin injection is often recommended as a first surgical step — before committing to anything permanent. It may be right for you if:

• Your fissure has been present for more than 6 weeks and hasn't responded to prescription creams or ointments
• You would prefer to try a non-surgical option before committing to a procedure that involves a permanent cut
• Your fissure keeps coming back after topical treatment
• Your fissure is associated with a tight, overactive sphincter muscle — whether it is at the front or the back of the anal canal
• You already have some difficulty with bowel control, and avoiding a permanent muscle cut is particularly important to you
• You have a Crohn's disease-associated fissure — in carefully selected cases, botulinum toxin can be a helpful option here too

Benefits

• No permanent cut to the sphincter muscle — so there is no long-term risk to your bowel control
• A day procedure under sedation or general anaesthetic — you go home the same day
• Good healing rates — around 50 to 75 in every 100 people are healed after a single injection
• If the first injection doesn't fully heal the fissure, it can be repeated — you don't have to jump straight to surgery
• A low rate of complications overall — this is a well-tolerated procedure
• If the injection isn't enough on its own, a lateral sphincterotomy (the surgical option) can follow — and you won't be starting from scratch in terms of healing

Risks & considerations

No procedure is without risk, and we want you to have a clear picture going in. Here is what to be aware of:

• The fissure may not fully heal after the first injection — this happens in around 25 to 50 in every 100 people. If that's the case for you, a repeat injection or a surgical option can be discussed. You won't be left without a next step.
• Temporary difficulty controlling wind — around 2 to 10 in every 100 people notice some reduced control of wind while the botulinum toxin is active. This resolves on its own as the toxin wears off after 3 to 4 months — it is not permanent.
• Bruising around the injection site — this is common and usually settles within 1 to 2 weeks.
• The fissure returning after the toxin wears off — around 20 to 30 in every 100 people see the fissure return within 2 years. If this happens, further treatment options are available and Mr Nguyen will discuss the best path forward with you.
• Spread of the toxin beyond the injection site — at the small doses used for fissure treatment, this is very rare.

Before the procedure

• No full bowel preparation is needed — occasionally a simple enema (a small, at-home wash-out) may be recommended; Mr Nguyen's team will let you know clearly if this applies to you
• Please arrange for a trusted adult to drive you home — you will not be able to drive yourself after sedation or a general anaesthetic
• Please let Mr Nguyen know if you have had botulinum toxin injections anywhere else in your body, or if you have a neuromuscular condition — this information is important for safe dosing
• You can continue using any prescription creams (such as diltiazem or GTN ointment) right up until the day of your procedure — don't stop them unless told to

On the day

• You will be admitted to the day-stay unit, and sedation or a general anaesthetic will be given. You will be relaxed and completely unaware during the procedure.
• Mr Nguyen performs an examination under anaesthetic first — carefully assessing your fissure and documenting its exact size and location while you are asleep
• Botulinum toxin is then injected into the internal anal sphincter through a very fine needle — the injection itself takes only a few seconds
• Both sides of the sphincter are injected to achieve the best possible muscle relaxation
• You will rest comfortably in the day-stay unit for 1 to 2 hours until you are ready to go home
• You will be sent home with a prescription for topical therapy and stool softeners to support healing over the coming weeks, along with written instructions

Recovery & aftercare

• Day 0 to 1: You may have mild soreness around the injection site — this is normal and eases quickly. Paracetamol and warm sitz baths (sitting in a few centimetres of warm water for 10 to 15 minutes) are very soothing.
• Days 3 to 7: As the botulinum toxin begins to take effect, the sphincter muscle gradually relaxes and the fissure pain starts to ease. Many people notice a real improvement during this window — it can feel like the pain finally starting to let go.
• 2 weeks: By this point, most people are experiencing noticeably less pain — including during and after bowel movements, which is often where the pain was worst.
• 3 months: This is when the botulinum toxin effect is naturally fading. Mr Nguyen will review how well your fissure has healed and discuss clearly what, if anything, you might need next.
• Throughout your recovery, keep your diet high in fibre and stay well hydrated — soft, easy-to-pass stools make a real difference to your comfort and to the healing process.
• If the fissure hasn't healed at your 3-month review, a lateral sphincterotomy (the surgical option) will be discussed with you — you won't be left without a clear plan.
• Mr Nguyen will see you for a routine follow-up appointment 2 to 6 weeks after your procedure. This review is provided at no charge.

Related patient guides

Plain-English articles written for patients and their families — good reading before or after your appointment, at whatever pace suits you.