How long will it take for my dexedrine (dextroamphetamine) effect to begin?

Very quick: The wonderful thing about stimulants is that they work essentially immediately. Once you find an effective dose, benefits should start 20-30 minutes after you take the medication and last, for dexedrine, (dextroamphetamine) probably about 8-10 hours, maybe a bit less. Similarly, benefit goes away about as quickly; typically benefit fades late in the day, & the medication is out of your body by next morning.

Dexedrine: Dexedrine (dextroamphetamine) is usually effective within 30 to 60 minutes (sometimes sooner).