According to the wiki and one of the possible quests, repeated use of stealthboys causes mental issues after only a few uses. Does the use of stealthboys affect the courier eventually? I don't use them enough to know. Thanks.

No, that is only the background of Nightkin and Stealthboys, you won't be affected by this.

Nonsense. It's a known fact that Stealth Boy use leaves to furtive behavior, kleptomania and homicide.

Doc Henry says it doesn't effect humans as it effects nightkin (or something like that, if I remember correctly).

Nightkin are super mutants, so they aren't all that stable to begin with. And they heavily abuse stealthboys, not just occasionally. Remember kids, everything in moderation!

Your character can't actually go insane, unless you roleplay him as such.

Dr. Henry's statement about it only effecting Nightkin/supermutants is a bit odd, because there are several earlier sources who claim that humans do develop schizophrenia from repeated use of stealthboys (I remember Fallout 1 and 3 at the very least touching upon it in some ingame document).
Still the Nightkins tendency to use them very often is no doubt the main reason it's very common among them.

ROFLMAO!! took me a few seconds but i finally got it.

There have been cases of humans going insane from stealth boy use:
http://fallout.wikia.com/wiki/Circle_of_Steel


Whether this becomes canon or not remains to be seen

It would be awesome if they did make your character go insane or something. Like, for no reason, without you controling it, your character would just start randomly headshotting people for no reason, or steal something at random, or twitch and rive like feral ghouls do because of massive mental instability.

But, something like this would probably be really hard to code and knowing the guys who made New Vegas, would be horribly glitchy and make the game crash.

They can make you go blind.