Jan 19 1812 Percy Bysshe Shelley

In the Biographical Sketch, at the beginning of The Complete Poetical Works of Percy Bysshe Shelley (New York: Houghton Mifflin, 1901), George Edward Woodberry notes a curious incident involving the poet: 

At Keswick, too, occurred the first of the personal assaults on Shelley, which tried the belief of his friends. He had begun the use of laudanum, as a relief from pain, but he had recovered from the illness which discloses this fact, before the incident occurred. On January 19, at seven o'clock at night, Shelley, hearing an unusual noise, went to the door and was struck to the ground and stunned by a blow. His landlord, alarmed by the noise, came to the scene, and the assailant fled. The affair was published in the local paper, and is spoken of by Harriet [his wife] as well as Shelley. Some of the neighbors disbelieved in it, but his simple chemical experiments had excited their minds and made him an object of suspicion, and it is to be said that the country was in a disturbed state.

Laudanum was a form of opium. It could be a potent narcotic. In the nineteenth century it was used in many patent medicines. It was prescribed for a variety of ailments. Samuel Taylor Coleridge was one of the famous laudanum addicts.