Effectiveness of Allopurinol in Reducing Mortality: Time-Related Biases in Observational Studies.

Observational studies are important to provide real-world data on medication effects. The observational studies showing significantly decreased mortality with allopurinol treatment cannot be used as evidence, however, mainly due to time-related biases that tend to greatly exaggerate the potential benefit of treatments. The ALL-HEART randomized trial, which is currently underway and evaluates the effect of adding allopurinol to usual care (compared to no added treatment), will provide reliable evidence on mortality.