Anticoagulants and antiplatelet agents, which interfere with blood coagulation, can lead to fatal bleeding. Moreover, their widespread use as drugs or rodenticides poses a high risk of accidental or intentional poisoning. Therefore, quantifying these substances is essential in forensic investigations. This research aimed to develop and validate a liquid chromatography-tandem mass spectrometry method capable of quantifying eighteen anticoagulant or antiplatelet compounds (apixaban, rivaroxaban, dabigatran, warfarin, acenocoumarol, fluindione, brodifacoum, bromadiolone, difenacoum, difethialone, chlorophacinone, coumatetralyl, flocoumafen, acetylsalicylic acid, clopidogrel, dipyridamole, ticagrelor, and ticlopidine) in a single run with simple sample preparation. The method was validated according to the FDA recommendations for all compounds, with an eight-min run time in human whole blood, the gold standard in toxicological forensic investigation. The method was also validated for therapeutic compounds and most rodenticides in bile and vitreous humor. Following validation, the method was applied to seven forensic cases with a known history of anticoagulant or antiplatelet agent use to prove the validity of the method. This method provides a valuable tool for legal contexts where precise determination of anticoagulant compound presence and concentration is required.