A science writer has won the right to rely on the defence of fair comment in a libel action, in a landmark ruling at the Court of Appeal.
Simon Singh was accused of libel by the British Chiropractic Association over an article in the Guardian in 2008.
Dr Singh questioned the claims of some chiropractors over the treatment of certain childhood conditions.
The High Court had said the words were fact not opinion - meaning Dr Singh could not use the fair comment defence.
However, the Lord Chief Justice Lord Judge, Master of the Rolls Lord Neuberger and Lord Justice Sedley ruled High Court judge Mr Justice Eady had "erred in his approach" last May, and allowed Dr Singh's appeal.
BBC News science correspondent Pallab Ghosh says that, had Justice Eady's ruling stood, it would have made it difficult for any scientist or science journalist to question claims made by companies or organisations without opening themselves up to a libel action that would be hard to win.
Dr Singh described the ruling as "brilliant", but added that the action had cost £200,000 "just to define the meaning of a few words".
"After two years of battling in this libel case, at last we've got a good decision. So instead of battling uphill we're fighting with the wind behind us," he said.
"The Court of Appeal's made a very wise decision, but it just shouldn't be so horrendously expensive for a journalist or an academic journal or a scientist to defend what they mean.
"That's why people back off from saying what they really mean."
The British Chiropractic Association said it was disappointed to lose the appeal but it was "not the end of the road".
BCA president Richard Brown said: "We are considering whether to seek permission to appeal to the Supreme Court and subsequently proceed to trial.
"Our original argument remains that our reputation has been damaged. The BCA brought this claim only to uphold its good name and protect its reputation, honesty and integrity".
In the article in April 2008, Dr Singh suggested there was a lack of evidence for the claims some chiropractors made on treating certain childhood conditions such as colic and asthma.
The BCA alleged that Dr Singh had effectively accused its leaders of knowingly supporting bogus treatments.
The case has become a cause celebre for the science community and led to calls for defamation law to be rewritten so it does not interfere with scientific debates.
His high-profile supporters include Stephen Fry, Ricky Gervais and Harry Hill, all from the world of entertainment.
Dr Singh said: "The judges are clearly unhappy on how libel laws can impact on discussion, on how this libel suit has quashed debate about chiropractics to a large extent.
"They're particularly unhappy about the way scientific discussion can be silenced by libel laws. That's a real boost to the libel reform campaign."
Coalition for Libel Reform spokeswoman Tracey Brown said: "This case has brought out of the woodwork the fact that so many other discussions are being killed, from discussions of cardiology to human rights to medicines.
"We're now pushing ahead for bigger changes to the law so that we have the kind of public interest defence that means it wouldn't have taken two years and £200,000 to find out whether Simon can defend himself."
British scientific organisation the Royal Institution welcomed the judgement.
Director of programmes Gail Cardew said: "It will encourage scientists and the public to discuss evidence freely without fear of legal threat."