As we mentioned, it's tempting to take a multisymptom cold medicine whenever you have some of the symptoms of a cold. Taking just one medication is simpler, safer and less expensive than buying multiples. Multisymptom medicines are great if you actually have all or most of the symptoms that they claim to treat. But if you don't, consider looking at more specialized medications.
The various types of cough syrups on the market are a good example of this. If you just have a dry, irritating cough, look for a medicine that only contains a cough suppressant. But if your cough also includes a sore throat, look for one that contains both a cough suppressant and acetaminophen to relieve the pain.
If you have congestion and a cough, look for a cough medication that also contains an expectorant (which loosens and thins mucus). What's the big deal about taking medicine that you don't really need? The potential side effects. An expectorant like guaifenesin, for example, can cause nausea and vomiting. At the very least, you could end up with very dry mucosal passages and chapped lips if you don't actually have thick mucus. So why risk the potentially unpleasant side effects of a drug that you didn't need in the first place?