Anticoagulants prevent the formation of harmful blood clots, which can cause a stroke, deep vein thrombosis (DVT), or pulmonary embolism (PE). Up to a few years ago, the only anticoagulant drug was warfarin. Warfarin remains the only option in certain situations (e.g. in patients with mechanical heart valves, significant mitral stenosis, or renal failure). However, in most indications (atrial fibrillation, deep vein thrombosis and pulmonary embolism), warfarin was replaced with newer drugs, direct oral anticoagulants (DOACs).

Four DOACs approved for use in the UK are apixaban, rivaroxaban, edoxaban, and dabigatran. Their main advantage over warfarin is that they don't require regular blood tests, which are necessary with warfarin to monitor the level of blood thinning (INR, international normalised ratio). Unlike warfarin, they are also not affected by the amount of vitamin K in the diet, and they have fewer interactions with other medicines. 

The main side effect of anticoagulant drugs is bruising and increased bleeding in even minor injuries. This may include cuts, nose bleeds, bleeding gums, red or dark-brown urine, red or black bowel movements, and for women, heavier bleeding during or outside periods.