Therapeutic drug monitoring is used to prevent or decrease the risk associated with the toxic effects of medication. This study aims to evaluate the potential advantages of Therapeutic Drug Monitoring (TDM) of subcutaneous Deferoxamine injection and prevention of clinical problems in β-thalassaemia major patients. Patients & Methods: Fifty-four thalassemia patients were allocated into two groups; missing, and not missing deferoxamine dose. TDM of Deferoxamine injection and it clinical outcomes was critically studied under the following subheadings: assessment of the adequacy of Deferoxamine usage, serum peak and trough concentrations of Deferoxamine and ferroxamine with needed pharmacokinetics, cardiac parameters and biomarkers, biochemical and hematological indices, adverse effects/toxicity, urinary assessment of Fe, Zn, selenium, and copper levels, compliance to treatment, dose adjustment in correlation to therapeutic index and life style. Results: Demographic data showed no significant difference. Peak plasma concentrations were 144.83±69 and 43.54±39.16 μg/L, while trough concentrations were 33±26.32 and 31.13±21.58 μg/L of Deferoxamine and ferroxamine, respectively. The elimination rate constant was 0.0237±0.00029 min^-1, half-life was 34 min, and distribution volume was 0.93±0.078. Although cardiac parameters showed no significant differences, there were significant differences in CK-MB, and hsCRP levels; troponin I value could not be detected. Biochemical and hematological studies showed significant differences in Ferritin B, urea, SGPT, SGOT, alkaline phosphatase, serum albumin and serum calcium. Assessment of adverse effects/toxicity showed significant differences. The correlation of serum ferritin to therapeutic index, and the life style including Vitamin C and/or E administration were assessed for the compliance to treatment. Conclusion: Therapeutic monitoring of chelation therapy by Deferoxamine in β-thalassemia patients is necessary to ensure effective treatment, compliance, and to avoid adverse side effects and toxicity.