The most common side effect of warfarin is bruising, as it increases the risk of bleeding. Other side effects may include gastrointestinal issues, but bruising is the most notable. Warfarin's blood-thinning effects make patients more prone to bleeding easily, leading to visible bruises. ;
The most common side effect of warfarin is bruising due to its blood-thinning properties, which increase bleeding susceptibility. Other side effects may include gastrointestinal issues, but these are less frequent. Therefore, the correct answer is A. Bruising.
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