Naiomi Louise Johns, 36, from Islington, fell from the bridge in Plaistow, east London, and was run over by a c2c train to Southend.
She suffered catastrophic injuries that a pathologist found would probably have caused instant death.
A coroner presiding over her inquest on Tuesday, June 17, described her death as “tragic”, but made clear there was no evidence it had been a suicide.
Naiomi, of City Road, was pronounced dead in the early hours of December 4 when railway workers discovered her remains on tracks near in Pelly Road, Newham.
Police retrieved grainy CCTV footage that recorded her fatal fall hours earlier, on the evening of December 3.
Cameras had captured her wandering around the streets with a barefoot, middle-aged man, whom police were never able to identify.
She was drinking from an orange carton, while he could be seen picking cigarette butts from the pavements.
After they parted ways, she was seen dragging a yellow street sign over to the bridge and using it to climb up and sit on the wall.
She was identifiable thanks to a white bandage around one of her legs, which was severely ulcerated due to persistent intravenous drug use, said senior coroner Graeme Irvine.
Medical records provided to the court detailed what he called “a long and entrenched history of substance misuse – cocaine, heroin and alcohol”.
She had been hospitalised the month before her death when her leg ulcers became infected.
“Miss Johns had a cocktail of drugs on board at the time of her death,” Mr Irvine told East London Coroner’s Court.
Toxicology tests found alcohol, heroin, crack cocaine, methadone and a painkiller called pregabalin in her system.
The drugs “would have affected her judgement”, the coroner said, and could have made her drowsy and been a factor in her falling onto the tracks.
He added that the drugs “probably would have acted as a behaviour disinhibitor”, influencing her “risky” decision to sit on the bridge parapet.
“There is no evidence before me that in the months prior to her death, suicidal thoughts had been expressed to anybody,” Mr Irvine concluded.
“There is nothing in her behaviour that is seen on the CCTV that suggests she was in in distress or dismay.
“It seems to me that it is just as likely that this was an accidental death.”
He recorded a narrative conclusion, saying it was “believed that she fell on to the railway tracks and was hit by a train”.
“I would like to offer my sincere condolences to Miss Johns’s family and friends,” said Mr Irvine.
“She was still a very young woman and her death must have come as a massive shock to them.”
