Here is what we know: If people take medications prescribed to them, they usually get better. But only about half of all patients prescribed medication take it according to directions. Here is what we don't know: We don't know how to get patients to take their medications, despite many studies looking at the issue.

Researchers doing a review for the international Cochrane Library for health information reviewed 182 trials that were testing different approaches to increasing medication adherence and patient health. Even though the review included many of the best quality studies, there were no clear winning solutions. In fact, many of the studies had problems in their design.

"The studies varied so much in terms of their design and their results that it would have been misleading to try to come up with general conclusions," said lead researcher Robby Nieuwlaat of the Department of Clinical Epidemiology and Biostatistics of the Michael G. DeGroote School of Medicine at McMaster University. "Based on this evidence, it is uncertain how adherence to medication can be consistently improved. We need to see larger and higher quality trials, which better take in account individual patient's problems with adherence."

Most trials were unreliable casting doubt on the validity of the results instead. Out of 182 trials, only 17 were of high quality and each of these tested combinations of several different approaches, such as support from family members or pharmacists, education and counselling. Still fewer, only five of these 17 showed improvements in health outcomes for patients, as well as in medication adherence.

"This review addresses one of the biggest challenges in health care," said Dr. David Tovey, Editor in Chief of the Cochrane Library. "It's a real surprise that the vast amount of research that has been done has not moved us further forward in our understanding of how to address this problem. With the costs of health care across the world increasing, we've never needed evidence to answer this question more than we do now."

The authors have now decided to turn to the research community to help understand the issues. They have created a database of the relevant trials and made this available to other researchers in the field in order to encourage collaboration and more in-depth analyses on smaller groups of trials.

"By making our comprehensive database available for sharing we hope to contribute to the design of better trials and interventions for medication adherence," said Nieuwlaat. "We need to avoid repeating the painful lessons of adherence research to date and begin with interventions that have shown some promise, or at least have not produced repeatedly negative results."