Yes you can mix it, but I would only use the Ritalin as a booster for the Adderall, and not try to get them to peak at the same time.....Ritalin being the stronger reuptake inhibitor of dopamine and Adderall being both the releaser of dopamine as well as the uptake inhibitor of both dopamine and norepinephrine, Ritalin could further reduce your bodys ability to break down the excess dopamine released by the Adderall.....It could be a recipe for overdose or toxicity if you use them at the peak of Adderall, but seem to be safe enough if you use it at the tail end of Adderall to prolong its effects.....In fact, some people are medically prescribed the combo of Ritalin and Amphetamine (Such as Adderall) safely.....Keep in mind that even a "regular" dose for an ADHD patient can be a huge dose for a noob and you dont necessarily need 'more' to get the desired effect. You can always add more later. Taking away requires an ambulance ride.
I am not using these recreationally or to substitute for an amphetamine addiction, but....I was recently prescribed Adderall XR 30mg, which is the same mg/day I had been taking of Ritalin which did nothing to improve my overall energy levels. I had 15mg of Ritalin in my system from the morning, then tried the Adderall as soon as I got it on the same day. I had no problems at all. It was fine.
For fatigue and narcolepsy Adderall works better. A lot better. A whole lot better. My dopamine is already depleted from a long term course of pain medication and I am in the tapering process. Ritalin is a dopamine reuptake inhibitor and I have low dopamine.....so it did very little for me. With Adderall its a weak reuptake inhibitor but a stronger releaser as well of dopamine. That is why Adderall will continue to work despite dopamine or adrenal fatigue better than ritalin or caffeine will.
I know this is an old thread, but I found it and the info was relevant for myself (before I decided to take it). What I am posting might be relevant to somebody else who needs this info.