I remember DayQuil being a lifesaver when I was in college in the early 00's and I needed to power through a day of classes with a bad cold. Then I remember at some point in the later 00's it just didn't work anymore (turns out they switched normal decongestant meds to phenylephrine in 2006). Once I found that out I started buying the behind-the-counter stuff with pseudoephedrine and it suddenly worked again. Not sure you need to be a pharmacist to figure this stuff out.