John Anthony Henry (11 March 1939, Greenwich, England – 8 May 2007) was a professor specialising in toxicology in the Faculty of Medicine, Imperial College London, at St Mary's Hospital in Paddington.
He insisted that cannabis was much more devastating than simple tobacco, taking away the user's free-will, dignity, and destroying personalities and damaging society.
He was called as an expert witness for the inquest into the death of Leah Betts, who died after drinking too much water after taking an ecstasy tablet at her 18th birthday party, and whose case became a cause célèbre.
He was the clinical toxicologist who dealt with the poisoning case of Russian dissident Alexander Litvinenko (at University College Hospital) in November 2006.
Professor Henry appeared numerous times on television, including Channel 4's Equinox, and Sky One's documentary entitled Poisoned - which primarily concentrated on the case of Ukrainian President, Viktor Yushchenko.
On one occasion Professor Henry even appeared on the Ali G show, having been told it was an educational programme, and talked about the dangers of hard drugs, brushing aside the jokes made at his expense.