Botulinum toxin is described in this episode as the deadliest natural substance in chemical literature, with an estimated lethal intravenous dose of 1.3 to 2.1 nanograms per kilogram, yet millions pay to have it injected into their faces. Its story begins in 1793 in Wildbad, Germany, when 13 people fell ill and six died after eating blood sausage stuffed into a pig’s stomach. Between 1817 and 1822 physician Justinus Kerner mapped the illness, noted it formed in airless conditions and paralyzed the nervous system, and predicted it might one day treat overactive nerves. In 1870 Müller coined botulism from the Latin for sausage, and in 1895 Émile van Ermengem isolated Clostridium botulinum after a funeral ham outbreak in Belgium.

The toxin destroys SNARE proteins so nerve endings cannot release acetylcholine. That made it a weapon studied at Fort Detrick and by Soviet and Iraqi programs, and later a medicine. Edward Schantz supplied purified toxin to researchers, ophthalmologist Alan B. Scott began treating crossed eyes in 1977 with a drug called Oculinum, and Allergan won approval in 1989 and renamed it Botox.

• Why a temporarily paralyzed eye muscle stays aligned after the toxin wears off
• Patients crossing into Canada when Oculinum lost its liability insurance in 1986
• Richard Clark’s 1989 forehead symmetry case and the Carruthers’ frown line study
• FDA approvals for cosmetic use in 2002 and chronic migraine in 2010
• Uses for sweating, spasticity, bladder and jaw clenching, and the 2009 boxed warnings