[2][3] After completing his early medical training at Birmingham, he joined the liver unit at London's Royal Free Hospital.
[4] Horton served as a medical columnist for The Observer and has written for The Times Literary Supplement and The New York Review of Books.
[4][5] In 2005, as a member of a working party set up by the Royal College of Physicians, he was the chief author of their report into the future of medical professionalism, "Doctors in Society".
[11] In 2016, he was appointed by United Nations Secretary-General Ban Ki-moon to an expert group advising the High-Level Commission on Health Employment and Economic Growth, which was co-chaired by presidents François Hollande of France and Jacob Zuma of South Africa.
[14] A few days after the worldwide mobilisation promoted by the activist movement Extinction Rebellion, Horton asserted in a video that health professionals should involve themselves directly.
[15] On 28 February 1998 Horton published a controversial paper by Andrew Wakefield and 12 co-authors with the title "Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children" suggesting that vaccines could cause autism.
[16] In the United Kingdom, the Health Protection Agency attributed a large measles outbreak in 2008 and 2009 to a concurrent drop in the number of children receiving the MMR vaccine.
"[20] However, there are groups criticising Horton for contributing to the ongoing dramatic drop of vaccination of children in Europe and America that causes several epidemics and deaths by delaying the retraction of the paper for 12 years.
[21] In the 11 May 2005 The Lancet, Horton criticized the British scientific group, the Royal Society, under Lord Rees for its neglect of medicine.
[22] Horton published an article in 2005 supporting paediatrician Roy Meadow who had been charged with serious professional misconduct by the GMC for giving erroneous and seriously misleading evidence in the Sally Clark trial.
With the support of erroneous statistical (and other) evidence from Meadow, the prosecution wrongly convicted her of murder and she spent over three years in prison before her successful second appeal.
[23][24] Her husband wrote a rebuttal letter to The Lancet in order to correct Horton's 'many inaccuracies and one-sided opinions' and to prevent them from prejudicing independent observers.
[25] The Clark family issued a statement addressing and countering with established fact each of the points making up Horton's biased support of Meadow.
[26] At the Time to Go Demo of 23 September 2006, Horton accused American president George W. Bush and British prime minister Tony Blair of lies and killing children in Iraq.
On 11 October, The Lancet published new estimates of the death toll of Iraqi citizens after the US-led invasion in 2003, putting it at a total of 655,000.
[38][39][40] Mark Pepys wrote: "The failure of the Manduca et al authors to disclose their extraordinary conflicts of interest… are the most serious, unprofessional and unethical errors.
The transparent effort to conceal this vicious and substantially mendacious partisan political diatribe as an innocent humanitarian appeal has no place in any serious publication, let alone a professional medical journal, and would disgrace even the lowest of the gutter press."
"[41] Horton's initial response to the outbreak of Coronavirus was cautious, telling his Twitter followers on 23 January 2020 that COVID-19 probably "has moderate transmissibility and relatively low pathogenicity."
"[44] On 18 March, Horton strongly criticised the Government's initial plans "to allow a controlled epidemic", saying: "Any numerate school student could make the calculation.
And, on 28 March, Horton's Lancet editorial stated that, having seen January's reports from China, the authorities "had a duty to immediately put the NHS and British public on high alert.