Hans Kristian Rausing, the heir to the £5.4bn Tetra Pak packaging fortune, has been arrested on suspicion of murdering his wife but is still not fit to be questioned, it emerged yesterday.

Mr Rausing, 49, was arrested on Monday though no evidence has yet emerged to suggest that his wife Eva, 48, whose body found in the bedroom of their central London home, was killed. Police are treating the death as "unexplained". Mr Rausing remains in a secure hospital where he is being treated for alcohol withdrawal.

Mrs Rausing, who has four children, may have lain undiscovered for days in the £50m five-storey Georgian townhouse at Cadogan Square, Belgravia, before she was found by police. A post-mortem proved inconclusive and further test results are due.

Detective Inspector Sharon Marman told the opening of an inquest into Mrs Rausing's death yesterday that Mr Rausing was stopped on suspicion of driving under the influence of alcohol or drugs on Monday. Police found drugs in the car and then discovered his wife's "lifeless body" when they searched the house.

Mr Rausing was arrested and is now under medical supervision. "He has been arrested on suspicion of her murder and we await notification of when he will be fit to be interviewed," said DI Marman. It is thought a decision will be made next week about when Mrs Rausing's body will be released. An autopsy has been carried out by a pathologist, with a second doctor present.

Mr Rausing, whose Swedish grandfather Ruben Rausing founded what became the world's largest food packaging company, was represented at Westminster Coroner's Court yesterday by Neil Saunders, QC. The philanpthropist, who did not enter the family business, and his wife, the daughter of a wealthy Pepsi Cola executive, have both struggled for many years with drug problems. In 2008, £2,000 of crack cocaine, cocaine and heroin was found at their home. Charges against them were dropped in return for their accepting a police caution.

The couple were arrested in April that year after Mrs Rausing was caught with drugs as she tried to enter a party at the US Embassy in London. Court documents revealed she was carrying about 10g of crack cocaine, 2.5g of heroin and 2.35g of diethylpropion – a banned stimulant and appetite suppressant. A further drugs stash was also found in her Renault Clio.

She confessed to making a "serious mistake, which I very much regret … I hope in due course to give purpose to get back on track and become the person I truly want to be".

Her family hired a surveillance team to shadow her at a cost of £100,000 a month, to disrupt any drug deals in a desperate attempt to protect her, the Daily Mirror reported yesterday.