I was prescribed 5mg tablet once a day. I've decided to start off with 2.5 mg a day to see how my body adjusts to the medication. I was would like to know if it would be wrong to only take the medication when needed - i.e. 2-3 times a week.

I have a very important exam coming up in 3 weeks and want to make sure I condition myself to get peak performance with little support from the medication.

Also, can anyone tell me how long it takes for the tablet to start working? and how long does it last?