How often should blood work be taken on children taking ADHD medications?

I put my son on ADHD medications after years of refusing to. He has been taking htem for roughly 3 months and she has not done any blood work on him. From what I understand it shoudl have been before he started and again in a few months. Any insight would be great, he has been going to her for 8 years but I am debating changing dr’s.
He was presrcibed Vyvanse which is a new ADHD medication.

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