"There is an enormous amount of interest in using meditation as a form of therapy to cope with a variety of modern-day health problems, especially hypertension, stress and chronic pain, but the majority of evidence that seems to support this notion is anecdotal, or it comes from poor quality studies," concluded researchers Maria Ospina and Kenneth Bond of the University of Alberta/Capital Health Evidence-based Practice Centre, in Edmonton.

They analyzed 813 studies focused on the impact of meditation on various conditions, including high blood pressure, cardiovascular disease and substance abuse.

Released Monday, the report looked at studies on five types of meditation practices: mantra meditation; mindfulness meditation; yoga, Tai Chi and Qi Gong.

Some of the studies suggested that certain types of meditation could help reduce blood pressure and stress and that yoga and other practices increased verbal creativity and reduced heart rate, blood pressure and cholesterol in healthy people.

However, the report authors said it isn't possible to draw any firm conclusions about the effects of meditation on health, because the existing studies are characterized by poor methodologies and other problems.

"Future research on meditation practices must be more rigorous in the design and execution of studies and in the analysis and reporting of results," Ospina said in a prepared statement.

Bond added that the new report doesn't prove that meditation has no therapeutic value, but it can inform medical practitioners that the "evidence is inconclusive regarding its effectiveness."

For the general public, the report "highlights that choosing to practice a particular meditation technique continues to rely solely on individual experiences and personal preferences, until more conclusive scientific evidence is produced," Ospina said.

The study was funded by the U.S. National Center for Complementary and Alternative Medicine in Bethesda, Md., part of the National Institutes of Health.