It is generally not recommended to take pseudoephedrine (found in Sudafed) together with DayQuil at the same time. DayQuil often contains a nasal decongestant (usually phenylephrine), and taking pseudoephedrine alongside it may lead to excessive stimulant effects such as increased heart rate and blood pressure. Both pseudoephedrine and the decongestant in DayQuil work similarly to narrow blood vessels and alleviate nasal congestion, so combining them can increase the risk of side effects like elevated blood pressure, heart rate, and potential heart problems. If you do need to take both, it's advised to space them apart by several hours and consult your healthcare provider, especially if you have underlying health conditions such as hypertension or heart disease. Also, monitor for symptoms like rapid heartbeat, dizziness, or insomnia if combining these drugs. In summary, taking pseudoephedrine with DayQuil is not usually recommended due to overlapping decongestant effects and potential for increased side effects, so professional medical advice is important before doing so.