Re: nervous about ritalin and drug testing
You must have a manual of regulations about your job. Does it say anything about mental health or psychiatric drugs? Taking a controlled substance ILLEGALLY is an automatic disqualification for a police officer, but legal use is different.
If there is no explicit policy against its use while on duty, they cannot just fire you for using Ritalin legally. They may, however, require you to report any medications you take, at which point you'd be on the hook for failing to report!
Now, depending on the attitudes of your superiors, disclosing ADHD may harm your career. Or, if your supervisor is more educated about mental health matters, and the Ritalin improves your performance, it might be okay. This is true in many fields, not just law enforcement, although it's particularly difficult in military and law enforcement careers.
Definitely, find some written policies. I looked around online but couldn't find them for you.