A psychiatrist who reviewed the case of Molly Russell told an inquest he was left sleepless after seeing the suicide material she watched on social media.
Molly, 14, took her own life in November 2017 after spending months browsing thousands of videos and images on platforms such as Instagram while battling depression.
An inquest into the death of the schoolgirl from Harrow, north-west London, is seeking to establish whether she was "overwhelmed" by the self-harm and suicide content.
On Tuesday, Dr Navin Venugopal told North London Coroner's Court that the dark material would have affected her state of mind. He had been instructed by the coroner to carry out a posthumous psychiatric evaluation of Molly, based on available evidence, which required him to look at the social media material.
He said: "I had to see it over a short period of time - it was very disturbing, distressing, there were periods when I wasn't able to sleep well for a few weeks.
"Bearing in mind the child saw this over a period of months I can say, bearing in mind she was already depressed, it would have certainly affected her and made her feel more helpless."
Andrew Walker, the coroner, had said of the videos and images: "This material seems to romanticise, glamourise and take the subject of self-harm - take it away from reality and make it seem almost unreal, take away from these terrible acts any kind of consequence."
He then asked the witness: "Can you see any positive benefit for that material being looked at? Dr Venugopal replied: "No, I do not."
'Likely that Molly was placed at risk'
There was a brief break in proceedings after Oliver Sanders KC, representing the Russell family, said they had become aware of a "rather unpleasant" Instagram account using Molly as its profile picture.
Caoilfhionn Gallagher KC, representing Meta, Instagram's parent company, asked for details of the account so the company could "take action immediately".
A spokesman for Meta later said: "This account has been removed from Instagram for violating our policies."
During the hearing, Dr Venugopal was also taken through several videos viewed by Molly, including one using "identical language" to that used in a note she made on her phone two days later.
He told the court: "If they are of that mindset and are seeing these sorts of things, it could have an impact."
In a separate written statement, he added: "I am of the opinion that it is likely that Ms Russell was placed at risk through accessing self-harm material on social media websites and using the internet. There was a risk to Ms Russell's health and mental state by looking at self-harm related content."
Senior executives from Instagram and Pinterest, the two social media platforms used by Molly the most, have apologised at the inquest for the content she was able to view. Judson Hoffman, of Pinterest, told the inquest the site was "not safe" when Molly used it.
However, Elizabeth Lagone, of Meta, said she believed posts that the Russell family believed encouraged suicide were in fact safe for teenagers to view.
The inquest continues.