Eight patients died following the poisoning at Stepping Hill hospital in Stockport, near Manchester in northwest England, in June and July 2011.
Victorino Chua, a 48-year-old father of two children, has been charged with murdering three of them — Tracey Arden, 44, Arnold Lancaster, 71, and Derek Weaver, 83.
He has also been charged with one count of causing grievous bodily harm with intent, 22 counts of attempting to cause grievous bodily harm with intent and eight offences of attempting to administer poison.
Assistant Chief Constable Steve Heywood of Greater Manchester Police said: “Our thoughts continue to be with those people who were deliberately poisoned and their families.
“From day one we made a commitment to those people, as well as the wider community, to thoroughly and robustly investigate what occurred.
“In close to three years we have conducted many painstaking inquiries and engaged with numerous medical experts. We are now at a point where we have charged Victorino Chua with a number of very serious offences.”