April 2 European Union lawmakers voted on Wednesday in favour of new rules that will ensure more open reporting of clinical trials results, even when they are negative, and also simplify the process for getting studies started.
The legislation approved by the European Parliament is expected to take effect in 2016 and will require results of all new clinical trials to be published within a year of the trial ending.
European Ombudsman Emily O'Reilly, whose office investigates complaints about maladministration in EU institutions, said the move was "a triumph for transparency" in European healthcare.
There has been a growing clamour for greater disclosure of detailed clinical trial results by pharmaceutical companies following a series of scandals over the safety of drugs such as Merck & Co's now withdrawn painkiller Vioxx.
A number of senior doctors have argued that in too many cases the decision on how and when to prescribe drugs relies on selective evidence controlled by manufacturers.
The new rules mean it will in future be possible for independent researchers to verify whether medicines are as safe and effective as they are claimed to be.
Ben Goldacre, a British doctor and author of "Bad Pharma", who has led a campaign called AllTrials urging study disclosure, welcomed the vote by parliamentarians as "an excellent small step forward".
But he remains concerned that the new EU Clinical Trials Regulation only covers new clinical trials and does not address access to full study results carried out on older medicines already on the market.
In addition to forcing greater transparency, the new law will also reduce the red tape surrounding the approval process for studies on medicines, including simplifying rules for running multinational trials.
Taken together, the measures should save research institutions and companies conducting clinical trials in the EU some 800 million euros ($1.10 billion) a year in regulatory costs, EU Health Commissioner Tonio Borg said in a statement.
($1 = 0.7263 Euros) (Reporting by Ben Hirschler, editing by David Evans)