Check what you are getting, because I am not aware of d-amphetamine (Dexedrine) being available in any 25 mg strength, extended-release or otherwise. For d-amphetamine extended-release, I know of the capsules of strengths 5 mg, 10 mg, and 15 mg. However, with mixed amphetamine salts (Adderall), I am fairly sure that a strength of 25 mg is available for extended-release preparations. So, make sure you know well and good what you are taking, for your sake.
Now, as for dosing, I would recommend keeping whatever is extended-release as it is - so, I'd advise against crushing the beads within the capsule. If we are talking about Adderall XR, than I would say your plan of splitting each 25 mg into three separate doses is not a bad one, however you could split 25 mg into five separate doses of 5 mg, which is what I would do, if I were you and wanted a good therapeutic amphetamine experience. With you having no amphetamine tolerance, you don't know how lucky you are. My first experience with amphetamines, at 5 mg Adderall XR, gave me loads of energy to focus into attention on whatever I wanted to do, as well as a glowing euphoria. The glowing euphoria seems to be something that never comes back after it is gone, and it goes away with chronic or frequent amphetamine use. So, please, you'll get to keep amphetamine a nice treat by using it sparingly. Another thing to be aware of, and this why I suggested an even lower dose for you, is that too high a dose of amphetamine will lead to paradoxical distractibility and an overabundance of hyperactivity/acceleration. If you were asking a good dose to use recreationally, and not for any studying help, I might suggest a dose of 10 mg Adderall XR, even 15 mg Adderall XR. But, doing this on a day you don't need to study may make the next time you study with a dose of 5 mg to help you along seem a bit underwhelming. Even for recreation, any amphetamine novice ought to know that less is, truly, much more. You don't want a tolerance, you don't want a habit, and you sure as hell don't want an addiction. That said, prudent use of amphetamine at modest doses for short periods of time, or without much frequency, can very much help the learning process and the ability to achieve related goals with ease and a sense of great reward. For the exam day, I would probably opt for dosing, as you would for studying (no increase needed), but have a few times with it, first, to feel it out, if you do, and only take it if you feel it is okay for you.
With no tolerance, you have the benefit of likely not having much any side-effect profile with low doses, but there are a few things you should know. You will want to be conscious to drink more water, and likely be rather thirsty, and this will lead to an increase in urinary frequency; no joke about that. But, really, on amphetamine keep hydrated, even if you have to use the restroom a lot more. Also, your appetite will likely be shot to hell, so make sure to keep sufficiently nourished, but at the same time, it is very unpleasant to force yourself to eat while the drug is most active, so feel it out, just make sure you are well and use common sense. I do find it more rewarding on a rather empty stomach, though, so I usually don't like to eat too much before I dose. Another thing I ought to mention is the comedown, which should be very mild at the doses I suggested with you being a novice to amphetamines, but as it wears off, you might feel a little anxious or uneasy, but you might have an afterglow - who knows. It won't be bad, though.
So, I hope this helps some. Ask questions, if you have any, and I will reply if able.
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