Generally yes — Sudafed (pseudoephedrine) and Tylenol (acetaminophen) work in different ways and are commonly taken together, but stick to the dosing on each label and ask a pharmacist, especially if you have heart, blood-pressure, or other health conditions.
Sudafed's active ingredient, pseudoephedrine, is a nasal decongestant that narrows blood vessels in the nose, while Tylenol's active ingredient, acetaminophen, relieves pain and reduces fever — they act through separate mechanisms and neither the NHS nor MedlinePlus flags a direct interaction between them. They are so unlikely to clash that they are routinely combined in a single "sinus and pain" product (MedlinePlus lists pseudoephedrine-plus-acetaminophen products such as Sudafed Triple Action and Tylenol Sinus Severe). The main real-world danger is not the pairing itself but accidental double-dosing: many cough, cold, and sinus remedies already contain acetaminophen (or pseudoephedrine), so the NHS advises checking the label before adding another painkiller. Taking too much acetaminophen can cause serious, even fatal, liver damage.
Read every label first: if your cold/sinus product already lists acetaminophen, do NOT add Tylenol on top, and likewise don't double up on pseudoephedrine. Keep total acetaminophen from all sources at or below the label limit — MedlinePlus says no more than 4,000 mg per 24 hours for adults (some Tylenol labels set a lower cap of 3,000 mg), and take less or avoid it if you have liver disease or drink three or more alcoholic drinks a day. Pseudoephedrine has its own cautions: talk to a doctor or pharmacist before using it if you have high blood pressure, heart disease, diabetes, thyroid disease, glaucoma, or trouble urinating from an enlarged prostate, and do not take it if you've used an MAO inhibitor antidepressant within the last two weeks. Watch for signs of too much acetaminophen (nausea, vomiting, upper-right belly pain, yellowing skin/eyes) or pseudoephedrine overstimulation (racing or pounding heart, nervousness, trouble sleeping, a spike in blood pressure), and seek care if these occur. When in doubt, ask a pharmacist to check your specific products and your health history.
This is general reference, not medical advice, and not a guarantee of safety. Interactions depend on your doses, health conditions, and other medicines. Always confirm with your pharmacist or doctor before combining products, and follow the dosing on each label.