Professor John Henry broke new ground in the management of poisoning and drug overdose.

He capped a distinguished career in medical academics with a seven-year tenure at Imperial College, London, and in his retirement continued as a medicolegal expert in the field of toxicology. He was sought for advice on the alleged ricin attack on the London Underground, and after the poisonings of the Ukranian opposition leader Viktor Yushchenko and the KGB agent turned dissident Alexander Litvinenko.

John Henry was born in 1939 to an Irish father who was a GP in London, a talented sportsman and also the team doctor for Millwall Football Club. A devout Roman Catholic, Henry joined Opus Dei in 1959 as a “numerary celibate member”, committing himself to a life of celibacy.

He was educated at St Joseph’s Academy at Black-heath, King’s College London and King’s College Hospital, from where he qualified as a member of the Royal College of Surgeons in 1964. In 1969 he developed a throat infection while on holiday in Italy, which was inadequately treated and eventually led to the onset of kidney failure. He gave up medicine for five years.

He received a successful transplant at the Royal Free Hospital in 1976, allowing him to return to medicine, becoming a medical registrar at Guy’s Hospital. He had become a member of the Royal College of Physicians in 1974, and was made Fellow in 1986.

He was consultant physician at Guy’s National Poisons Information Service from 1982 to 1997, the year he was appointed professor of Accident & Emergency Medicine at Imperial College. He was also head-hunted by St Mary’s Hospital in Paddington, West London, becoming honorary consultant in accident and emergency medicine there. During this time he was also honorary senior lecturer in clinical pharmacology and clinical adviser, United Medical and Dental Schools.

At Imperial, Henry saved the lives of many patients from drug overdose. His own experience as a dialysis patient for more than seven years made him deeply empathetic to those in his care.

He was first and foremost a very gifted teacher who could explain complex medical matters in simple, logical terms. He was incisively brilliant as a toxicologist and would spot relevant clinical symptoms and signs long before others.

Among his many achievements was introducing the fatal toxicity index for antidepressants, which changed prescribing practice. He described the hyperthermic and hyponatraemic complications of methylen-edioxymethamphetamine, and demonstrated the mechanism of the latter in Ecstasy poisoning. He pioneered the introduction of alpha1 acid glycoprotein as an antidote for drug toxicity, particularly cocaine and tricyclic antidepressants, and he introduced a new near-patient test for salicylate and paracetamol.

Henry was chief medical editor of the BMA Guide to Medicines and Drugs(now in its sixth edition). He was often called upon as an expert witness in court cases involving toxicological issues and drug misuse, and gave advice on setting European priorities for drug research and to the Home Office and royal colleges on drug misuse. He was also involved in the guidelines on self-harm drawn up for the National Institute for Health and Clinical Excellence (NICE) in 2004, and the Royal College of Psychiatrists and Association of Forensic Medicine report on substance misuse by detainees in police custody in 2005.

Henry was an expert witness at the inquest into the death of Leah Betts, who had died after taking Ecstasy on her 18th birthday. He willingly gave expert advice to journalists and in January 2003 poured cold water on an alarmist report of a planned ricin attack on the London Underground by pointing out that ricin would be fatal only if injected into the blood stream.

He also suggested that the Ukrainian political leader Viktor Yushchenko had been poisoned by dioxin, because of the characteristic pattern of acne, missed by the doctors in Vienna, and also gave opinions about the fatal poisoning in London of Alexander Litvinenko.

He was a rare example of a brilliant scientist who, in between saving lives in his hospital, invested time and energy into ensuring that the British public got the best possible information from the media about his areas of expertise.

He was not interested in process but rather the welfare of patients, and especially in the ways by which drugs could devastate the young. His keenness to impart this message led to his being misled into appearing on the comedy show Ali G, Aiiiin 2000, answering mischievous questions about class-A drugs.

Henry had a very strong will and did not pay court to either convention or to petty rules and regulations unless they suited him. He had been director of Netherhall House, a Roman Catholic residence, between 1968-1969, and he lived there in his last years. He was extremely cheerful with an always-positive attitude to life.

Professor John Henry, toxicologist, was born on March 11, 1939. He died of complications from the removal of a kidney on May 8, 2007, aged 68