Doctors are increasingly encouraged to factor costs into their drug prescribing decisions but very few clinical trials actually detail these costs, a Canadian study has found.

The research team led by Michael Allan from the Department of Family Medicine at the University of Alberta in Edmonton randomly sampled 188 randomised controlled trials (RCTs) published between 2003 and 2005 in six high-impact general medical journals.

These were the New England Journal of Medicine, the Journal of the American Medical Association, the Lancet, the British Medical Journal, the Annals of Internal Medicine and the Archives of Internal Medicine. The results of the analysis were published online in the open-access journal PLoS ONE.

Only 52 (27.7%) of these articles made any mention of costs, while just 14 (7.4%) mentioned actual costs of drugs or other healthcare – defined as a cost with a numerical value in dollars, pounds or another currency. Actual drug costs appeared in only nine or 4.7% of the published RCTs.

Logistic regression analysis indicated that funding was the only factor associated with the inclusion of actual costs or any mention of costs in the articles. Industry-funded studies were significantly less likely to mention costs than trials funded solely by non-profit sources, the researchers found. Indeed, the likelihood of cost information being included in the RCTs grew as the degree of industry funding declined.

Trials with any mention of costs increased across the funding sources from 18% for industry-backed trials to 31% for those with mixed funding and 36% for studies funded by non-profit organisations. This trend was consistent with the findings for actual costs: industry funding 1%, mixed 7% and non-profit 15%.

In almost all the member countries of the Organisation for Economic Co-operation and Development, the costs of pharmaceuticals are increasing faster than any other component of healthcare budgets, Allan et al say.

“Ideally, physicians would select less expensive products if the alternatives were equally efficacious,” they comment. “Unfortunately, physicians have a very limited understanding of drug cost and, more importantly, do not understand the large cost differential between expensive and inexpensive drugs.”

Authors of industry-funded trials may avoid discussion of costs because these products are usually more expensive, the researchers note. On the other hand, it may be that authors of non-profit funded trials “are more likely to include a discussion of costs because they feel obliged to consider costs as many non-profit sources (like government-linked sponsors) may be more cost-conscious”.