I am a 54 year old female. I have been on and off methylphenidate SR(sustained release) 20mg for several years and it has always started to wear off after 3-4 hours. I've always taken it 2-3 times a day, depending on how long my day is going to be. I have also tried the regular release, but it "hits too hard" and "drops off" too quickly for me. I have tried other stimulants and methylphenidate SR seems to work best for me. Most people have to try different meds and doses for a while to find what works for them. Good luck.