Karl Law, 34, a builder from Fareham, Hampshire, went missing on a night out during his cousin's stag celebrations in the Czech capital in November.
His body was found in the River Vltava in December.
Coroner David Horsey concluded Mr Law had probably fallen into the river and had been unable to save himself.
He said he believed the account of a woman who reported seeing Mr Law in the city almost 24 hours after he was last seen by his friends.
The reported sighting was close to where Mr Law's body was found, the coroner's court in Portsmouth heard.
Mr Horsey said the witness described the builder as being heavily intoxicated, but he said exactly what happened remained "something of a mystery".
Mr Law was in Prague for Lee Cross's stag weekend, along with 12 other men.
Mr Cross, who had been due to marry in December, postponed his wedding until March.
After his disappearance Mr Law's family led a search campaign in the city and hired a private investigator.
A man found dead in a river in Prague after a stag weekend had been drinking heavily and had taken several lines of cocaine, an inquest has heard.