Google and Amazon must act after a British woman made a suicide pact with two people she met online and bought the poison that killed her on the internet, a coroner has said.

Chloe Macdermott, 43, died on 23 May 2021 after buying a lethal substance from the US on Amazon. She had been struggling with her mental health for several years before she began researching ways to end her life on an online forum, an inquest at inner west London coroner’s court was told this month.

Two days before her death, she “formed an association” with two people with whom she planned suicide. A day later, she contacted them while her husband was away and “an agreement was made to act that night”. She ingested the substance at about midnight and died from its effects the next morning.

The coroner Paul Rogers recorded a conclusion of suicide and issued a prevention of future deaths report to Google and Amazon, saying he believes they have the power to prevent another similar tragedy.

The report has also been sent to the home, health and culture secretaries and the national lead for suicide prevention at the National Police Chiefs’ Council.

Rogers said it was a matter of concern that the forum that Macdermott used and others like it “encourage suicide, assist it by provision of information about suicide methods, counsel suicide by providing information about it and thereby potentially facilitate the commission of a criminal offence in the United Kingdom”.

He said: “[The forum, whose name was redacted] permits material to be exchanged and viewed within its open chatrooms whereby suicide is encouraged, assisted, counselled and procured through the provision and exchange of information and methods.

“No age or other restrictions are in place to prevent access to children, vulnerable teenagers and vulnerable adults. No prominent signposting is in place to organisations from whom help is available to prevent suicide. Posts are made by users containing details of methods of suicide without any effective administration to remove such harmful content.”

The availability of the poison online and the ability of Britons to have it delivered from the US “without effective border and/or custom controls” was also a matter of concern, Rogers said.

All organisations that the coroner has written to must respond within 56 days. They must outline the action they intend to take to prevent future deaths and a timetable for doing so. If no action is proposed, they must explain why.

• In the UK and Ireland, Samaritans can be contacted on freephone 116 123, or email [email protected] or [email protected]. In the US, you can call or text the National Suicide Prevention Lifeline on 988, chat on 988lifeline.org, or text HOME to 741741 to connect with a crisis counselor. In Australia, the crisis support service Lifeline is 13 11 14. Other international helplines can be found at befrienders.org