Previous work has shown that, when a drug study was
funded by the company that made that drug, the results
might be biased in favour of that drug because the methods
or analyses were manipulated.
New research shows that, for blood pressure drugs,
studies are now much less likely to have biased results
but still tend to have overly positive conclusions favouring
the company's products.
The authors call on editors and peer reviewers to scrutinise
the conclusions of these studies to ensure that they contain
an unbiased interpretation of the results.
Meta-analyses represent the highest level of research
evidence in the hierarchy of study types. They pool data
from multiple studies to provide summary statistics on
the effectiveness of a given treatment. They have a great
deal of influence on patient care and healthcare policy
and drug companies have started to reference meta-analyses
in their advertisements.
Previous studies have shown that randomised controlled
trials with financial ties to single drug companies are
more likely to have results and conclusions that favour
the sponsor's products, and a recent study suggests that
the same holds true for meta-analyses.
So researchers in the US set out to determine whether
financial ties with single drug companies are associated
with favourable results or conclusions in meta-analyses
on blood pressure lowering (antihypertensive) therapies.
A total of 124 meta-analyses were included in the study,
49 (40%) of which had single drug company financial ties.
Differences in study design and quality were measured.
Meta-analyses with single drug company financial ties
were not associated with favourable results but were significantly
more likely to have favourable conclusions, even when
differences in study quality were taken into account.
In fact, the data show that studies funded by a single
drug company have a 55% rate of favourable results that
is transformed into a 92% rate for favourable conclusions,
representing a 37% gap. The gap shrinks to 21% (57% to
79%) when two or more drug companies provide support.
Yet the gap vanishes entirely for studies done by non-profit
institutions alone or even in conjunction with drug companies.
These findings suggest a disconnect between the data
that underlie the results and the interpretation or "spin"
of these data that constitutes the conclusions, say the
The findings also expose a failure of peer review, add
the authors, and should act as a wake-up call to editors
and peer reviewers, as well as to policy-makers, meta-analysts,
and readers. All of these groups should closely scrutinise
the conclusions of meta-analyses to ensure that they contain
an unbiased interpretation of results, they conclude.
The clear inference from this study is that impartial
studies are more reliable, say researchers in an accompanying
editorial. However, rather than imposing legal restrictions
on drug company funding or participation in these studies,
they suggest that doctors should be warned to be cautious
in interpreting the conclusions of studies.
The full research article is published in the British
Medical Journal website.