'I'm surprised Eva survived the 80s,' says Rausing's friend

Drug problem dated back to her student days when she was studying pharmacology

Eva Rausing, one of Britain's richest women who was found dead of a suspected drugs overdose at her £50m Chelsea home last week, had been "lucky to survive the 1980s", according to an old friend.

Last night her husband, heir to the £5.4bn Tetra Pak fortune, remained in a secure medical facility awaiting questioning after being arrested on suspicion of her murder.

Ms Rausing's drug dependency is thought to date back to her time at Occidental College, a liberal arts centre in Los Angeles attended by Barack Obama. It is there that Mrs Rausing, who studied pharmacology, was first introduced to hard drugs. She graduated in 1986.

Yesterday former fellow students and friends paid tribute. Tom Maguire, a Hollywood music writer, wrote: "Sadly, the thing that surprised me the most ... is that Eva survived the Eighties. Lovely girl who I hung out with quite often."

Mrs Rausing, 48, may have been dead for up to a week before her body was found on Monday. Hans Kristian, her husband, was arrested four days later amid reports that the couple had turned part of their home into a "drugs den" and were living in just two rooms.

Police remained outside the front door yesterday. Among the tributes littering the porch was a small bouquet with the message: "Dear Eva, I will never forget your friendship and kindness. Nicky."

Mr Rousing is believed to be unfit to be questioned after being diagnosed with alcohol withdrawal and a suspected breakdown. He remains under police watch.

The cause of Mrs Rausing's death has yet to be established.

The couple had a troubled history of substance abuse. After studying at Garden House School and the American School in London, Eva met her husband at Farm Place, a £2,000-a-week rehabilitation centre near the capital. The couple became anti-drug advocates, donating millions of pounds into raising awareness of its dangers and set up their own drug charity.

Mentor UK benefited from their quiet generosity. The organisation's mission is to prevent young people from ever experimenting with drugs, a cause that Mrs Rausing promoted publicly.

Eric Carlin, its founder, said she argued against policy reforms aimed at liberalising drug laws. "She said that the more access to drugs she had, the more she would take. She said she couldn't help herself and believed that you needed to ensure that people, especially young people, did not have access to drugs at all.

"She was a lovely, lovely woman but she was conscious from her own experience that once you become addicted, it's a long way back and some people can't get better."

In 2008, she was cautioned after being found in possession of crack and heroin during a security search at a party in the US Embassy in Grosvenor Square.

Sir Ian Blair, the Met Commissioner, described the decision not to prosecute as "very surprising" and said it "sends entirely the wrong message about drug use".

In a statement after her arrest in 2008, Ms Rausing said: "I have made a serious mistake which I very much regret. I intend to leave as soon as possible to seek the help that I very much need.

"I have made a grave error and I consider myself to have taken a wrong turn in the course of my life. I am very sorry for the upset I have caused. I thank my family and friends for their kindness and understanding."