Adderall tolerance (and stimulant tolerance in general) does not work in the same way that other drugs do.
Part of amphetamine (adderall) tolerance is simply due to both mental and physical exhaustion. I.e., a person staying up all night continuously taking doses of amphetamine finds that at 7 am the next day, the dose they just took isn't doing anything. However, cessation of use for a few days (or even a few weeks) usually fixes this problem.
Long term amphetamine tolerance, however, is caused by amphetamine physically changing a person's brain chemistry (sometimes permanently), such that they not only can no longer experience euphoria from their 'regular' amphetamine dose, but also have a higher threshold for pleasure in their day to day life even without drugs.
This long term tolerance usually coincides with permanent psychiatric disorders; making amphetamines a very dangerous, devastating, and life ruining drug when it comes to long term use.
However, it is not all bad news for an amphetamine user; a simple act of "mind over matter" can itself cure amphetamine tolerance. If an individual is able to learn how to alter their mind's own expectations, they can manipulate their brain chemistry and alter the effectiveness of their amphetamine. This leads to the strange result of a user being able to increase euphoria simply by "expecting" it -this inadvertently causes a correlation with mood; if a person is in a good mood ( have had quality sleep, are relaxed, are physically healthy, etc), they will notice better results from amphetamine use.
This also provokes questions as to whether or not the "body load" (the negative physical effects of amphetamine) plays any role in tolerance. For example, any amphetamine formulations containing the levo isomer (such as adderall xr) would produce more of a body load and therefore increase tolerance more than amphetamine formulations where the levo isomer is absent. Perhaps the brain establishes a correlation between the negative physical effects (which are damaging to the body) and the positive psychological effects (euphoria, alertness, etc) and therefore cancels out the positive effects to try and prevent the negative effects. Perhaps the brain even sabotages its own reward system simply to try and avoid the physical damage that amphetamine causes.
Yet another theory would be that since amphetamine activates reward pathways, the brain requires a higher source of pleasure in order for the same level of euphoria to be felt again - thereby requiring a higher dose.
There also seems to be a ceiling effect in play (especially with levo isomer formulations) where a higher dose will no longer produce more positive effects and instead only increases negative ones. I myself, being an avid user of adderall xr, never found my dose going higher than 120mg before all I was doing was increasing negative physical effects.
Having used amphetamine on a very frequent basis for the past 2 and a half years, my 'regular' dose is still 90mg (I take a 30mg xr, wait 10 minutes then take another 30mg, then wait 45 minutes to an hour before taking a third 30mg; I find that my amphetamine kicks in the smoothest this way)
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Still, the 'glow' I experienced from first using amphetamine (being able to get high off 20mg xr) has never again returned, even after long breaks; however, decent euphoria is still always achievable with less than 100mg so long as circumstances are right.