The odds of vomiting your pills, enduring significant pain, and then having a seizure that you may recover fully from or end up with permanent disability is much greater than your odds of successfully ctb. I wouldn't recommend this method.
Aggregate data on drug poisonings suggests that
when all drug types are considered it
is about 1.5% effective for ctb. The aggregate data includes drugs more reliable than ritalin so the odds specific to ritalin & dexedrine are probably significantly lower than 1.5%.
Generally speaking dexedrine and methylphenidate (the drug in ritalin) are not considered very lethal according to population studies even though they carry a high potential for serious/painful cardiac emergencies in high doses. Stimulant overdose deaths usually occur in people with years of stimulant abuse whose hearts are already failing, and even then many of them die slowly while in hospital.
It's not impossible but you're playing the lottery against high odds of being rendered incapacitated, in greater pain, and unable to ctb using more peaceful methods.