TSH level, because hypothyroidism is a well-established cause of galactorrhea and should be assessed before attributing symptoms to the antipsychotic.

While hypothyroidism can cause mild prolactin elevation, the clinical context (risperidone use) makes medication-induced hyperprolactinemia far more likely.

LH and FSH levels to evaluate for primary pituitary pathology such as a prolactinoma causing the galactorrhea symptoms.

LH/FSH may be assessed later if pituitary pathology is suspected, but the medication history makes this a lower priority than confirming the prolactin level.

Testosterone level, because breast tenderness and galactorrhea in a male suggest hypogonadism as the primary underlying etiology.

Testosterone may be secondarily affected by chronic hyperprolactinemia, but it is not the first-line assessment.

Prolactin level, as risperidone is among the highest prolactin-elevating SGAs and is the most likely cause.

Risperidone is among the highest prolactin-elevating SGAs due to its potent D2 antagonism and poor blood-brain barrier penetration at the pituitary. A prolactin level confirms the diagnosis and quantifies the severity. If prolactin is markedly elevated (>100-200 ng/mL), pituitary imaging may be warranted to rule out a prolactinoma — though medication-induced elevation is far more likely in this context. These findings inform subsequent treatment planning decisions.