Can i take some nyquil after a relatively large dose of ritalin (methylphenidate)?

Not recommended : Nyquil typically has dextromethorphan to suppress coughing in addition to an antihistamine. Combining all of those meds together, especially the cough med, can lead to interactions and unpleasant side effects that may last for hours. When using an otc med be as symptom specific as possible and avoid meds that have multiple ingredients. Hold the stimulant when using otc cold meds.

Possibly: Is your relatively large of Ritalin (methylphenidate) prescribed by a doctor? Taking a sedating substance like Nyquil once should not cause any harm. However, if you are experiencing difficulty with sleep initiation from a prescribed dose of Ritalin (methylphenidate), speak to your prescriber about a different dose or a different medication.