A British backpacker who was found dead on a popular Thai tourist island had consumed a potentially fatal combination of alcohol and Valium, police said Tuesday citing preliminary autopsy data.

The body of Christina Annesley, 23, was discovered in a bungalow on Koh Tao, southern Thailand, last Wednesday.

"The initial results from the autopsy found Valium and alcohol in the victim's body," Thai police spokesman Lieutenant General Prawut Thavornsiri, told AFP.

"There were no signs of rape," he added, saying the full autopsy results would be released within three days.

Annesley's death came four months after a British couple were found murdered on the same island in a case that placed local police under intense pressure.

Two Burmese nationals have been charged for the murder of David Miller, 24, and the rape and murder of Hannah Witheridge, 23 -- but both men have retracted their confessions saying they were obtained under duress.

Officers were also heavily criticised for allowing locals and journalists to walk over the crime scene.

Police in Koh Tao have said there was no evidence of foul play in the bungalow room where Annesley was discovered.

But in an indication that they wanted to avoid any criticism over their handling of the case, her body was sent to Bangkok for a full autopsy, which was carried out Sunday.

Many of Annesley's final tweets -- under the handle @chrstinadarling -- spoke of the beauty of Koh Tao's white sand beaches and azure waters, which are popular backpackers and divers.

She also made reference to taking both Tramadol, a painkiller, and Valium, an anti-anxiety medication, in the days leading up to her death.

Last week Koh Tao police said they had found three kinds of medicine in her room, but no illicit drugs.

British daily The Telegraph said Christina's mother Margaret had posted on her daughter's Facebook page saying she had died of "natural causes".

Tourism is a mainstay of Thailand's economy, which has struggled despite the military promising to turn the country's financial fortunes around after they took over in a May coup following months of street protests.