A coroner called for tighter controls on selling lethal drugs over the internet after hearing that Isobel Narayan, 16, came across the substance having searched online forums about suicide.

Nigel Meadows said he would be writing to the Chief Pharmaceutical officer to see if anything could be done to tighten regulations about access to harmful drugs.

He said policing the internet was "virtually impossible" but it was a "matter of public concern" that Isobel was able to get hold of the drug.

Isobel, the daughter of a barrister, was found dead by her parents at their home in Didsbury, Manchester, in December 2011.

An inquest heard that there was nothing to suggest she was unhappy but a police interrogation of her computer revealed she suffered "misplaced" and "unfathomable" feelings of low self-esteem and worthlessness.

She had ordered a drug online and in the months before her death had looked up forums giving guidance on assisted suicide for people with terminal illnesses, Manchester Coroner's Court heard.

Isobel wrote a document entitled: "Reasons why I should kill myself or why my life is not worth living", the hearing was told.

Her father, Harry Narayan, a barrister and crown court recorder in Manchester, told the inquest his youngest daughter, who had gained top marks at GCSE, was top of her year in physics and studying A-levels with the hope of studying to be a vet like her older sister, Freya.

A keen horse-rider she was also on the student council at Xaverian College in Manchester but was "so able", her studies did not really challenge her and she craved more homework to do.

There had been a "mini crisis of confidence" the month before she died, he said, but Bell, as he called her, returned to college a week later and got back into the rhythm of student life with everything appearing normal.

He said on the night before the tragedy Freya had gone out and he had waited up for her.

He said: "I stayed up waiting for Freya to come back in the early hours of the morning. At 1am, I heard Bell cleaning her teeth in the downstairs bathroom. I said, 'Are you all right'? Everything was normal."

The inquest heard that around noon, Mrs Nayaran went upstairs to rouse Isobel to see if she wanted a bacon brunch.

Mr Narayan added: "Anne went to ask her about a bacon butty and came back down and asked if I could go and see her. She was dead."

The parents raced up to her room where Isobel was lying on the top bunk of her bed, which has a desk underneath.

He added: "She was lying in her usual sleeping position right arm over her head. I felt her forehead and it was cold.

"I remember everything vividly. She had a bucket which I use when I clean the house, there was a bit of liquid in it. There was a Listerine bottle on her top bunk and there was a tumbler on the window sill that had some dried powder on it.

"She must've got the bucket some time after I heard her at 1am", she said.

Mr Narayan said he had spoken to his daughter about boys, pregnancy and bullying, but there was nothing in her life to suggest she was unhappy or worried.

Det Insp Kevin Marriott, from Greater Manchester Police (GMP) who investigated the death, said searches of her computer found she had made inquiries about obtaining the drug and around a month before her death a quantity was posted to her in two packages.

The hearing was told that Isobel had gone on forums and discussed “the use of the drugs and quantities and dosages and uses and guidance and sources of advice for those people wishing to harm themselves".

There was also a pamphlet available online designed for those with terminal illnesses who want to end their lives.

Det Insp Marriott said that while Isobel had low esteem, the “self-deprecating comments” she made in the document "Reasons why I should kill myself" were “totally misplaced”. He added: “It's unfathomable."

Ruling that the teenager killed herself, Mr Meadows, the Manchester coroner, said: “There were no indications that she was even contemplating taking her own life. There's no clue or indication that anything was untoward whatsoever."

He said it was "inevitable" in such cases loved ones will ask themselves if they could have noticed something wrong, but said there was nothing Isobel’s family should reproach themselves for.

He said: "It's a strange time of life for teenagers. There's hormones raging, there's pressures."