First off, we have not done this. But I do have some thoughts:
What were the contraindications for stimulants? Were they expected to have low therapeutic effectiveness, or to have serious side effects? There's a big difference between those two rationales for being not recommended. Some of the serious considerations against psychostimulants for certain individuals include suicidality (e.g., in persons at risk for mood disorders, especially depression), and substance abuse (in persons at risk for addictive behavior). Those are factors that often would also be picked up in the family medical history. When you read about common side effects of psychostimulants for the general population, these serious ones might not be as relevant.
As to the genetics, there is an increasingly rich pool of big data-generated correlations between certain profiles and certain complex traits. But like any emerging technology, there is also still uncertainty. Is it hard and fast reliable? Depends on your personal definition of hard and fast, range considered reliable, and assumption of risk.
