A patient died a week after attending the Stapleford private clinic for heroin addicts when he was sent away with a "DIY home detox kit", the General Medical Council (GMC) was told yesterday.

Evidence at the hearing, which may determine the future direction of drug addiction treatment, alleged that the kits should never have been used in a setting where there was no trained medical care.

The man, 29, who was known to the hearing as Mr GS, choked on his vomit while asleep after taking the mix of drugs.

Instructions issued by Colin Brewer, the clinic's medical director, to the man's mother on how to use the DIY kit of 16 different drugs were "unclear, confusing and inadequate", the GMC heard. The treatment involved sedating the patient - which carried a risk of aspiration of vomit - and his mother should have been told that the extra drugs he was prescribed were alternatives, rather than additional, to his other medication. The man was found dead in September 2001, after taking drugs including diazepam, rohypnol and temazepam.

It was claimed yesterday that seven doctors - six men and one woman, including theStapleford Centre's founder Dr Brewer - had handed out the wrong medicines, prescribed excessive quantities and provided "confusing" instructions to a patient who died after taking his prescription. It is the biggest case to come before the GMC in its 145-year history and will ask profound questions of the liberal school of heroin treatment. A number of addicts turned up at the GMC venue in London for the hearing yesterday morning to defend the centre, which has branches in Belgravia, central London, and Stapleford Tawney, Essex. One woman said she feared for her husband's life if it closed.

The seven doctors are accused of serious professional misconduct for their controversial treatment of drug addicts. They are alleged to have misprescribed medicine by issuing excessive amounts and the wrong types, as well as providing irresponsible combinations of drugs, such as methadone and rohypnol.

Allegations also include failure to take steps to ensure that the prescribed drugs could not be sold on to others and claims that patients were not properly monitored. It is believed the clinic was operating a policy of "maintenance" prescriptions, in contrast to the NHS's tougher approach to weaning addicts off drugs. Dr Brewer, 62, also faces allegations that he tried to interfere with two potential expert witnesses in 2001.

The professional conduct committee was also told how Dr Brewer's treatment of a heroin addict in 1997 failed to take into account the fact that the woman, 26, had become pregnant, had had a fit and was suffering from depression. He is accused of serious professional misconduct in relation to 13 patients since May 1990.

The other six doctors are Anthony Haines, Hugh Kindness, Nicolette Mervitz, Martin O'Rawe, Ronald Tovey and Timothy Willocks. In total the allegations relate to 16 patients. Dr Brewer did not attend yesterday's hearing.

Ian Harris, 52, a Stapleford patient from Dagenham, east London, turned up to support the doctors. He said: "The reality for many [patients] will be they will be at the mercy of drug dealers and some will resort to crime or prostitution in order to stop horrendous side effects. Their health will be weakened beyond belief." Mr Harris's wife, Jill, said: "If they lose their licence, I fear for Ian's life." The case is expected to last for 50 days.