^That's a possibility.
Another thing to consider is that stimulants are known to work really well for people in the beginning then drop off. So they start off working extremely effectively for depression, perhaps anxiety all of sorts, fatigue, and in general. Some people find that these effects are maintained (though almost always at a lower level than they worked for in the beginning). When one increases the dose, some of these benefits may come back, but the higher the dose, in general, the less of a chance that these benefits will continue.
That's basically how people get strung out on adderall: the drug tricks them into believing that a little more, then a little more, then a little more, will satiate themselves. And this is how stimulants function as very moreish substances.
Each time the dose is raised, too, there is greater potential for psychosis, which is itself the highest form of anxiety. So things like thinking the police are after them (which is ironic, because that's possibly the case), people are out to kill them, or maybe that their food is being intentionally poisoned. In fact, in extreme cases, MDPV (the ingredient in many "bath salts") and similar stimulants create just completely chaotic behavior. People in that state literally have to be tackled by several policemen or shot many times with a taser before they stop fighting. Remember the guy in the states that starting biting someone's face off? Yeah...
