Bobbi Kristina Brown was addicted to drugs by the age of 14, a new book has claimed.

Author Ian Halperin's unauthorised biography 'Whitney & Bobbi Kristina: The Deadly Price of Fame' alleges the 22-year-old aspiring actress - who has been in a coma since January after being found unconscious in her bath - was committed to a psychiatric hospital shortly before she turned 15 for trying to slash her wrists and stab her mother, Whitney Houston, and claimed the late 'I Will Always Love You' singer was too consumed by her own drug problem to help her daughter.

Following Whitney's death in 2012, Bobbi's behaviour became even more ''reckless''.

A source said: ''The past couple of years she hung with a bunch of crazies, they were wild and reckless.''

Insiders also speculated to the author - who has previously written controversial books about stars including Michael Jackson, Brad Pitt and Angelina Jolie - that the troubled star was found in her bath because she had been subjected to ''the plunge'', where overdose victims are submerged in cold water and slapped to try and revive him.

A local drug addict told Halperin: ''She probably took the plunge.''

The author added: ''He told me that when somebody 'drops' - a term meaning to OD - there are all kinds of ways to revive them. 'I've never seen it done in a bath,' he said to me, 'but I sort of helped bring somebody around with a cold shower. You stick them under the cold water and you slap them to bring them around.'

''This could explain the facial bruises that paramedics reportedly found.''