Botox® is the trade name for botulinum toxin. In its pure form, botulinum toxin is a type of food poisoning that causes muscle weakness. It acts as a nerve impulse blocker, preventing muscles from contracting. In an extremely dilute form, botulinum toxin has many medical applications.

Botulinum toxin can be injected directly into the muscles of the face or eye when facial muscles are overactive. Botox® causes the overactive muscles to relax. It usually takes a few days for the therapeutic effect to be noticeable. The injections may need to be repeated every 4 to 6 months.

Botulinum toxin is used in ocular conditions such as blepharospasm, an excessive contraction of the eyelid muscles that forces the eyelids closed, and hemifacial spasm, an excessive contraction of the facial muscles on just one side of the face. For certain types of double vision, botulinum toxin can be injected directly into the eye muscle opposite the paralyzed eye muscle. Some wrinkles also become less prominent if injected with botulinum.

Side effects of the injection are temporary. They can include a droopy upper eyelid, double vision, and inability to close the eyelids.