There are also people that drink coffee to calm down. I believe those with ADD or/and ADHD are in that group?
They help everyone, kinda. Problem is they also flood the brain with neurotransmitters (dopamine, especially), causing other undesirable effects. But for people whose brains are... 'wired' in a certain way (ADHD, ADD, some ASD), they help much more than they hurt, letting them function more 'normally' (for a given society's definition of normalcy) .
The standard mediation for ADHD and ADD (and sometimes off-label for ASD, it depends) is some kind of stimulant, basically a class of drug with similar effects as meth (coffee is also a stimulant, incidentally). The so-called gold standard (especially in older literature) is amphetamine (e.g. Adderall), which is basically meth with one less 'attached' chemical group. Amphetamine was also the stimulant drug (along with meth) widely (mis)used in World War II.
Meth itself may even be prescribed sometimes. This is rare, because it has nastier side effects compared to the others, but sometimes it just works. Interestingly, a specific mirror image of meth (the 'left'-handed variant; most other therapeutic/recreational applications use a mix of both) is also used as a nasal decongestant; this has far less potential for euphoria or abuse, though it still has some stimulant properties.
(And it will cause you to fail drug tests because most of them don't distinguish between the drug mirror images.)
Another consideration is that... well... these drugs are all stimulants, so they will still speed up your heart rate regardless of your neurochemistry. So, taking them on a long-term basis is probably not good for your heart (even in approved therapeutic doses). But this is a trade-off; some people will have to take them to even function 'normally' in society (or to not fall behind), which is why the doctor will prescribe them (they know the risks well, and shouldn't prescribe them nilly-willy, but you know, sometimes it happens).
Fair enough. An ADD here with some level of neurosis (Anxiety and stress ain't fun in extreme doses). Used Concerta before, but that didn't sit well with me. Imagine sweating like you were climbing a mountain constantly and your limbs feeling cold 24/7. Tried various other stuff with the doctor over . Ended up on a mixture of Strattera for everyday stuff (good for anxiety and such, helped focus a bit as well) and Ritalin for the times I really needed to focus on work/studying though I haven't used that one for months.
Personally, I have never drunk coffee before (just personal choice). But heard from other folk with similar stuff (my father for example) that it helped them calm down and relax during evenings and such, hence my previous comment.