[deadA1ias]

Take a look at Modafinil. Not a traditional stimulant. I've been taking it routinely at the start of the workday for focus with great success. No "come down".

[balfirevic]

Are you worried about building up tolerance? Although not 100% clear, it looks like it might potentially be an issue:

https://www.gwern.net/Modafinil#tolerance