Not everyone with Asperger's has to take Ritalin. You should talk to the doctor that did your dx.
Ritalin is not a treatment but it helps relieve some symptoms like impulsiveness and distraction: Something not every Asperger has.
You should not take Ritalin unless prescribed, because as most medication, its a toxic for the liver, and if you take other medications or alcohol with it, it increases the chances of liver toxicity. Your doctor should decide if taking Ritalin's positive aspects outweight the negative ones.
Also, for the people that take Ritalin without needing it, there is something called paradoxical effect (at least thats the translation i can make from spanish, my main language). What Ritalin does is basically improve the usage of Dopamine by your body. People who take Ritalin usually have low amounts of Dopamine. However, Dopamine is a stimulant neurotransmitter, so if you take it when you don't need it, instead of making you more focused, you get get the opposite effect: You become less concentrated, hyperactive and excited, and it also accelerates your heart rate.
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Autodiagnosed textbook BPD