Botulinum toxin is a protein and neurotoxin produced by the bacterium Clostridium botulinum. Popularly known by one of its trade names, Botox, it is used for various cosmetic and medical procedures. Botulinum can be absorbed from eyes, mucous membranes, respiratory tract or non-intact skin.

Blepharospasm and strabismus
In the early 1980s, university-based ophthalmologists in the U.S.A. and Canada further refined the use of botulinum toxin as a therapeutic agent. By 1985, a scientific protocol of injection sites and dosage had been empirically determined for treatment of blepharospasm and strabismus.[12] Side effects were deemed to be rare, mild and treatable.[13] The beneficial effects of the injection lasted only 4–6 months. Thus, blepharospasm patients required re-injection two or three times a year.
In 1986, Scott's micro-manufacturer and distributor of Botox was no longer able to supply the drug because of an inability to obtain product liability insurance. Patients became desperate as supplies of Botox were gradually consumed, forcing him to abandon patients who would have been due for their next injection. For a period of four months, American blepharospasm patients had to arrange to have their injections performed by participating doctors at Canadian eye centers until the liability issues could be resolved.[14]
In December 1989, Botox, manufactured by Allergan, Inc., was approved by the U.S. Food and Drug Administration (FDA) for the treatment of strabismus, blepharospasm, and hemifacial spasm in patients over 12 years old.[15]

Cosmetic
The cosmetic effect of BTX-A on wrinkles was originally documented by a plastic surgeon from Sacramento, California, Dr. Richard Clark, and published in the journal Plastic and Reconstructive Surgery in 1989.[16] Canadian husband and wife ophthalmologist and dermatologist physicians Carruthers JD and Carruthers JA were the first to publish a study on BTX-A for the treatment of glabellar frown lines in 1992.[17] Similar effects had reportedly been observed by a number of independent groups (Brin, and the Columbia University group). After formal trials, on April 12, 2002, the FDA announced regulatory approval of botulinum toxin type A (Botox Cosmetic) to temporarily improve the appearance of moderate-to-severe frown lines between the eyebrows (glabellar lines).[18] Subsequently, cosmetic use of botulinum toxin type A has become widespread with many celebrities viewing it as less intrusive and/or artificial than other types of plastic surgery.[19] The results of cosmetic procedures vary but can last up to eight months.[20] The U.S. Food and Drug Administration approved an alternative product-safety testing method in response to increasing public concern that LD50 testing was required for each batch sold in the market.[21] [22]

Muscle spasms
The acceptance of BTX-A use for the treatment of muscle pain disorders is growing, with approvals pending in many European countries. The efficacy of BTX-A in treating a variety of other medical conditions (including prostatic dysfunction, asthma, and others) is an area of continued study.

Upper motor neuron syndrome
BTX-A is now a common treatment for muscles affected by the upper motor neuron syndrome such as cerebral palsy, for muscles with an impaired ability to effectively lengthen. Muscles affected by the Upper Motor Neuron Syndrome frequently are limited by weakness, loss of reciprocal inhibition, decreased movement control and hypertonicity (including spasticity). Joint motion may be restricted by severe muscle imbalance related to the Upper Motor Neuron Syndrome, when some muscles are markedly hypertonic, and lack effective active lengthening. Injecting an overactive muscle to decrease its level of contraction can allow improved reciprocal motion, and so improved ability to move and exercise. In June 2009, its use for treating hypertonic muscles helped an Australian man to walk again. He had required a wheelchair for mobility following a stroke 20 years prior.[23]

Sweating
While treating patients with hemifacial spasm at Southend Hospital in England in 1993, Khalaf Bushara and David Park were the first to show that botulinum toxin injections inhibit sweating.[11] This was the first demonstration of non-muscular use of BTX-A. Bushara further showed the efficacy of botulinum toxin in treating hyperhidrosis (excessive sweating). BTX-A was later approved for the treatment of excessive underarm sweating.

Cervical dystonia
Botulinum Toxin Type B (BTX-B) received FDA approval for treatment of cervical dystonia on December 21, 2000. Trade names for BTX-B are Myobloc in the United States, and Neurobloc in the European Union.[citation needed]

Chronic migraine
OnabotulinumtoxinA (trade name Botox) received FDA approval for treatment of chronic migraines on October 15, 2010. The toxin is injected into the head and neck to treat these chronic headaches. Approval followed evidence presented to the agency from two studies funded by Allergan, Inc. showing a very slight improvement in incidence of chronic migraines for migraine sufferers undergoing the Botox treatment.[24][25]
Since then, several randomized control trials have shown Botulinum Toxin Type A to improve headache symptoms and quailty of life when used prophylactically for patients with chronic migraine[26] who exhibit headache characteristics consistent with: pressure perceived from outside source, shorter total duration of chronic migraines (<30 years), "detoxification" of patients with co-existing chronic daily headache due to medication overuse, no current history of other preventative headache medications.[27]