The Metropolitan Police said officers on patrol in the Cambridge Circus area detained a man at around 11.20pm on Saturday, September 20, following a report of a theft.
A spokesperson for the Met said the man “subsequently became unwell.”
Officers gave first aid and called for paramedics.
He was taken to hospital, where he remains in a stable condition.
A cordon was in place last night at Romilly Street but has since been lifted.