How long does this pill work?

i take 2 10 mg pills of dextroamphetamine in the morning and then kinda as needed through out the day (usually 15 mg around noon and 15 again around 3). Sometimes 20mg will actually make me high (purely unintentional) until 3pm and i won't take anymore pills for the rest of the day. Other days i can take the full 50mg and i feel as if i could have used more. I don't know what the deal is, but i used to take the ER form and the high feelings and side effects were more predictable (as in i knew what not to take in order to avoid them). Seeing as the release was more extended, or "smooth" as my Dr. says, it didn't make me high at inopportune times (like at work, which is very unnerving and unpleasant). The disadvantage was the ER form didn't work as intended or as well, and i didn't get that immediate "punch" that i needed of the intended consequences of the drug. If everything goes as normal 20mg lasts me from about 8-11 or 12 or 3-4 hours, but i have a high tolerance to drugs usually.

The duration of effect of 30 mg (PO, orally) mixed amphetamine salts of a single entity (generic for Adderall) in tablet form - immediate release - typically ranges from 4 to 6 hours.

Duration of effect and plasma concentrations of amphetamines are increased dramatically with co-adminstration of antacids, particularly sodium bicarbonate. Conversely, acidifying agents commonly found in juices, coffee, and caffeinated beverages may decrease this drug's efficacy. There are many variables which can determine how long any drug "lasts": tolerance, metabolism, age, sex, BMI, and (if) any other concurrent medications an individual takes.

If you're taking this for the first time, even under close medical supervision during initial titration, the side-effects should be expected to be prolonged and intensified. Adverse effects and, for many, positive or beneficial effects of amphetamines will most likely subside as your body adjusts to the medication. [Any dosage modification should be under the exclusive direction of your physician.]