Background <p>Migraine is a neurovascular disorder involving serotonergic, vascular, metabolic and haematological pathways. Peripheral serotonin has been implicated in migraine biology, but its relationship with glycaemic and haematological markers remains unclear. This study evaluated serum serotonin in migraine and examined associations with clinical, glycaemic and haematological variables.</p> Methods <p>This comparative cross-sectional study included 74 adults with migraine diagnosed using International Classification of Headache Disorders, 3rd edition criteria and 82 non-migraine controls from a tertiary-care teaching hospital. Demographic data, anthropometry, blood pressure, pulse rate, fasting glucose, HbA1c, estimated average glucose, haemoglobin, thyroid-stimulating hormone and serotonin were recorded. Group comparisons used t-tests and age-adjusted analysis of covariance. Pearson and partial correlations assessed serotonin associations. Multiple regression used estimated average glucose in the primary model and HbA1c in a sensitivity model, as estimated average glucose is derived from HbA1c.</p> Results <p>Among 156 participants, the migraine group was older and had higher blood pressure, pulse rate, fasting glucose and HbA1c/estimated average glucose, with lower haemoglobin. Serum serotonin was lower in migraine than control participants (10.72 ± 5.42 vs. 88.43 ± 6.26 ng/mL; <i>p</i> &lt; 0.001), remaining significant after age adjustment. Serotonin correlated inversely with HbA1c/estimated average glucose, fasting glucose, blood pressure and pulse rate, and positively with haemoglobin. In multivariable analysis, estimated average glucose, haemoglobin and age were independently associated with serotonin.</p> Conclusions <p>Adults with migraine showed lower peripheral serotonin and altered glycaemic, haemodynamic and haematological profiles. These exploratory findings require validation in longitudinal studies with detailed migraine phenotyping.</p>