Injections of botulinum toxin (Botox) may help heal a tear (fissure) in the anus.

The internal anal sphincter, one of two muscles that control the anus, is always under tension. If this tension (also called resting pressure) is too high, spasms and reduced blood flow can cause an anal fissure or prevent an existing one from healing. Botulinum toxin, the poison that causes botulism, temporarily paralyzes the internal anal sphincter. This reduces the spasm and allows the fissure to heal.

Botulinum injections may be more helpful than nitroglycerin ointment, but the studies do not all agree.^{1, 2} A review of many studies showed that injections of botulinum toxin were no better at healing anal fissure than nitroglycerin ointment.³ Fissures may return after treatment with Botox is discontinued.

Side effects of botulinum injections may include the inability to control the passage of gas (gas incontinence), pain from the injections, bleeding, infection at the injection site, and fecal incontinence. Most people do not have any side effects.⁴

Botulinum toxin injections can be expensive.