Clinical trials that show negative treatment effects are less likely to be published in scientific journals, which could have important implications for healthcare, a new review from the Cochrane Library has found.

According to an international team of researchers, trials showing positive treatment effects with important or striking findings are much more likely to be published.

"This publication bias has important implications for healthcare. Unless both positive and negative findings from clinical trials are made available, it is impossible to make a fair assessment of a drug's safety and efficacy," said lead researcher, Sally Hopewell of the UK Cochrane Centre in Oxford.

The team carried out a systematic review of all the existing research in this area. They found that negative results were published less often and if these results were eventually published, they took up to four years longer to appear in journals compared to studies showing positive results.

The reason most commonly given for not publishing was that investigators thought their findings were not interesting enough or did not have time.

"The registration of all clinical trial protocols before they start should make it easier to identify where we are missing results," said one of the researchers, Kay Dickersin from Johns Hopkins University in Baltimore, US.

The team pointed out that the registration of trials and their results ‘would help people conducting systematic reviews to look at both published and unpublished evidence to reach reliable conclusions’.

The researchers emphasised that their review highlights the need for a worldwide commitment to the disclosure of the findings of clinical trials.

“The World Health Organisation recently found widespread support for the development of such a process,” commented researcher, Mike Clarke of Trinity College Dublin.

The team added that healthcare decisions need to be based on all the evidence, ‘not just the most exciting results’.