Is it okay to take brahmi and dextroamphetamine at the same time?

Probably. No suggestion of a negative interaction between the two that i can find in any of my resources. But, be sure to let your prescribing doctor know what else you are taking when using herbal supplements.
Supplements - carefu. I was not able to find a contraindication of using the two together. However, there is no governmental oversight of supplements so you cannot depend on purity, dose, quality and other factors.