The timing of medications might influence their safety, or their effectiveness. When this project began, warfarin was recommended for evening use, but no studies had evaluated whether warfarin timing actually mattered. INRange organized 236 volunteer family physicians in 54 western Canadian communities to invite their warfarin-using patients (217 of whom participated) to randomly determine the time of day they would use warfarin (morning or evening) for the next 7 months. Warfarin's effectiveness was determined by how often the "INR" blood test (a common test measuring how fast blood clots) was in the desired range. At the end of the study there was no meaningful difference between groups.
Warfarin should be taken whenever regular compliance would be easiest.