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Introduction: The Institute for Safe Medication Practices (ISMP) lists heparin as a high-alert medication due to its risk of causing significant patient harm. Our institution utilizes weight-based heparin dosing protocols to increase safety, but these nomograms only provide guidance for adults weighing greater than 40-50 kg, depending on indication. This study looks to evaluate anticoagulation in low-weight patients receiving therapeutic heparin and to characterize heparin prescribing patterns within our network. Methods: This retrospective health record review evaluated patients admitted from 01/2022 to 12/2024. Patients included were adults weighing less than 40 kg who received titratable or continuous heparin or less than 50 kg and received Lower Intensity heparin. The primary outcome was median time to reach a target aPTT or anti-Xa range, which was indicative of therapeutic anticoagulation. Secondary outcomes were the percentage of patients who achieved therapeutic anticoagulation, percentage of aPTT or anti-Xa levels within therapeutic range after therapeutic anticoagulation had been reached, documented bleeding event, and a description of heparin prescribing patterns. Bleeding events were identified according to International Society of Thrombosis and Haemostasis (ISTH) definitions of major and clinically relevant non-major bleeds. Results: The final analysis included 102 patients and 117 infusions. The median time to achieve therapeutic anticoagulation was 19.5 hours. Therapeutic anticoagulation was achieved with 52% of infusions. After therapeutic range was first reached, 52% of aPTT or anti-Xa levels remained within range. There were 8 major bleeds and 9 clinically relevant non-major bleeds. Within the Lower Intensity group, 53% of initial infusions were started at the recommended rate for patients weighing 50 kg instead of the patient’s actual weight. Conclusions: Among low-weight adult patients who received therapeutic heparin, half did not achieve therapeutic anticoagulation. Those who did required more than 19 hours on average to do so. More than half of initial infusion rates for the Lower Intensity group were higher than the recommended weight-based rate. Further research is warranted to find the most effective regimen to implement standardized dosing protocols for this patient population.