The large US Women's Health Initiative trial was stopped prematurely in 2002 after showing an increased risk of cardiovascular events from combined hormone replacement therapy.
However, well before the Women's Health Initiative trial was published, the authors analysed 23 small trials of hormone replacement therapies and found that they were not as protective as the observational data had shown. Many of these trials were done by pharmaceutical companies to obtain drug licences and were not publicly available.
When they published their findings in 1997, they were ridiculed. But extra data from six further studies confirmed their concerns. High Court dispensation was required to access these trials.
If trials done by pharmaceutical companies for licensing purposes had to include adequate data on harms and ineffectiveness, we could learn much more quickly what we need to know about new drugs, say the authors.
Regulators should require drug manufacturers to record adverse events and make the results public, they conclude.