The 15-year-old girl was unconscious at the Princess Royal Hospital, Haywards Heath, for seven hours.
She and another girl of 15 were illegally sold peach schnapps, Budweiser, and Bacardi.
Now police have warned they will get tough on licensees who sell drink to under-age youngsters.
Stuart Payne, 21, of Hamsey Road, Sharpthorne, then trainee manager at the Wine Rack store in London Road, Burgess Hill, was found guilty of serving the girls last November and fined £200.
He denied the offence and told Mid Sussex magistrates he did not think they were under-age.
But Ann Toynbee, prosecuting, said he should have requested proof of their age.
The court heard that the girls were among a group in St Johns Park, Burgess Hill.
Court chairman Alan Forbes said the results of Payne's actions could have been "catastrophic" for the girl who needed treatment.
PC Jon Lelliott, the officer in the case, said after the hearing that he spent a lot of time dealing with under-age drinking in the summer.
He said: "We are often just confiscating this stuff and pouring it away in front of them."
sHe warned licensees: "We still reserve the right to send in under-age people in conjunction with Trading Standards officers to check premises."
Converted for the new archive on 30 June 2000. Some images and formatting may have been lost in the conversion.
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