Can nyquil which has tylenol, (acetaminophen) detromethorphan, and doxylamine succinate in it affect my Coumadin or pt/int levels. I've had a bad stomach virus?

Maybe. Could have, but more likely from dehydration and not eating.
A valuable resource. You can use a drug interaction checker whenever you have questions about drug-drug interactions or drug - food interactions. Here is one option (Drugs.Com): Your pharmacist is also an excellent source of information.

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