Can i cut a methylin (ritalin) 10 mg in half?

Im a 27 yr old female and was diagnosed the end of last yr for ADHD combined type. I've been on 3 different meds that made me more crazy then I already was. Ritalin has been working some what and now we r trying to figure out the right dosage that works for me. This wk my dosage from 20mg increased to 30 mg a day. She said I can take 2 10mg in the morning when I need more focus and one 10 mg in the evening. But the 20mg actually works for me so I'm thinking of cutting a 10mg in half and taking a full pill and half of another one twice a day. But I heard that I should cut them. I have a pill cutter so should I or will I end up in the ER?