Yes.

From the ATF, the following categories of persons are prohibited: > who is convicted in any court of a crime punishable by imprisonment for a term exceeding one year;
> who is a fugitive from justice;
who is an unlawful user of or addicted to any controlled substance (as defined in section 102 of the Controlled Substances Act, codified at 21 U.S.C. § 802);
> who has been adjudicated as a mental defective or has been committed to any mental institution;
> who is an illegal alien;
> who has been discharged from the Armed Forces under dishonorable conditions;
> who has renounced his or her United States citizenship;
> who is subject to a court order restraining the person from harassing, stalking, or threatening an intimate partner or child of the intimate partner; or
> who has been convicted of a misdemeanor crime of domestic violence.

As someone with a legit prescription for ritalin, you are not an unlawful user of or considered to be addicted to a controlled substance.