"i have been taking ritalin for almost 3 years &amp; it has been great. i had adhd in high school &amp; college. i couldn&#039;t focus, listen to lectures, read well or study. i saw a doctor during college &amp; he prescribed me ritalin 20mg 3x/day (i had long days in college). i was finally able to read well, study &amp; focus. i love learning now, i&#039;m motivated &amp; my mood improved. now i take 20mg 2x/day (i graduated &amp; go to bed earlier). it lasts around 4 hours. i never experience withdrawal or major sleepiness when i don&#039;t take it. side effects: difficulty sleeping if taken too close to bed time &amp; appetite loss (minor). i highly suggest an eating schedule and drinking lots of water so you don&#039;t eat too little. i would often forget to eat in the beginning."