Well, per [1], it increases dopamine, norepinephrine, serotonin, and other chemicals in the brain. It is highly unlikely that it has no effect on one's decision making (esp. when you take it when you are _not_ very tired). It's more likely that you don't notice the effects, but the effects would likely be measurable.

It's the same with caffeine. I'd wager a guess that most people don't think it influences their decision making... And yet it seems it does (e.g. [2]).

[1] https://www.sciencedirect.com/topics/medicine-and-dentistry/...

[2] https://www.freethink.com/health/does-caffeine-harm-your-dec...

Modafinil increases my risk-taking behavior much more than amphetamine does, though otherwise has much lower physical side effects than amphetamine. Took me awhile to realize I was being incredibly flirty due to modafinil. It was typically well-received and it took me a long time to realize that it was modifying my behavior. But once I knew what to look for I saw the modifications across wide parts of my life including work and personal goals. Generally made me take on more ambitious goals.

Eventually I suffered some traumatic events and modafinil started causing anxiety, especially when mixed with caffeine, and I found vyvanse was better after that for managing my ADHD without quite as much paralyzing anxiety.

Everyone’s brain reacts very differently to each stimulant. On the very rare occasion that I take cocaine I usually just fall asleep and enjoy a hard nap! I don’t experience about 90% of the effects my friends report from it.

Caffeine keeps me awake all night long even if I have just half of a cup of coffee any time after 11AM, and increases my anxiety to the point where it’s very difficult to be productive.

Dextroamphetamine and Vyvanse both affect work productivity similarly for me but dextroamphetamine shuts down my social interaction, whereas Vyvanse increases it. This is particularly strange because they “should” be the exact same active drug once the Vyvanse is metabolized. Biology is still very much being discovered and there is a lot that we just don’t know yet.

I remember reading a study on modafinil that found people on modafinil for a couple days when giving directions where apt to be irritable and not throwing in identifying details.

so a modafinil user "Go three blocks that way, turn left, go two blocks turn left again, turn right immediately"

non-modafinil user "Go that way until you see the Circle-K, turn left, then it's two blocks where you have to turn left again, the street name is something like Majors way, and then the first time you can turn after that you turn right - there's a large drawing of a man drinking coffee on the side of the building"

on edit: unfortunately no idea where I read this but that was a big let-down for me as it implied there was perhaps no such thing as a free ride. Bummer.

Very much underestimate the impact of exhaustion. If I recall correctly, I read a study that driving after a long day of work was many times more dangerous than driving over the legal limit for alcohol. Kind of puts both into perspective