First off, the effectiveness in diagnosed add / ADHD people vs people just using it doesn't seem to be 1:1. For example, it gets me focused on relevant tasks, whereas my non ADHD friends could easily get sucked into the infamous "clean the entire house" funnel. Or, it just makes them anxious.
I also suspect it dramatically reduces my emotional reaction to things, including art. I feel like it robotocizes me. Sure, I'm more effective, but time seems to just slide by without having any real impact on me. The weeks I don't take it seem to automatically be more "colorful" in my long term memory.
It's certainly made my life a hell of a lot easier as someone with ADHD, but I wouldn't sing its praises as a side-effect-less drug. If anything, the side effects are insidious in a dangerous (emotionally) and undetectable way.
Modafinil, sold under the brand name Provigil among others, is a medication to treat sleepiness due to narcolepsy, shift work sleep disorder, or obstructive sleep apnea (OSA).[3][7] In OSA continuous positive airway pressure is the preferred treatment.[3] While it has seen off-label use as a purported cognitive enhancer, the research on its effectiveness for this use is not conclusive.[8][9] It is taken by mouth.[3]
You can buy it online, legally in the US anyways, probably in Aussieland too.