In our house, it is an age-old argument. What IS the difference? As I understand it, a cold triggers the cells to overproduce histine which leads to an abundance of histamine which, supposedly, makes our noses run, etc. So, it seems logical an antihistamine is the answer. Yet, a decongestant does not contain antihistamine!
So, what’s the deal here? Any SDopers in pharmacy or bio-chem?
No, but at first glance, it seems a decongestant is used to relieve swollen membranes or blockage, and an antihistamine would be what you would use to prevent histamine like you said from allergies or colds.
Right, decongestants generally work by vasoconstriction, in which they tighten the blood vessels to reduce their leakage of blood serum (which is the mechanism by which mucus membranes excrete), whereas antihistamines generally work by blocking one of the several steps in the immune system’s histamine response.
As others have said, antihistamine medicines may be of some use for symptoms due to allergy. Although, by virtue of the near-ubiquitous presence of antihistamines in cold and flu remedies, the drug companies would have you believe they’re also of benefit in those conditions as well, there is, in fact, virtually no evidence that antihistamines are effective to relieve the symptoms of colds.
At the bottom of this page, is a beautifully concise summary* of the evidence with respect to antihistamines and the common cold. As you can see, there really is not very much evidence at all. I’ll point out that you’re more likely to be sedated by antihistamines than you are to obtain relief of cold symptoms from them. Indeed, their purported benefit may simply be a result of people “mistaking” ease of sleep following their use rather than their effectiveness in treating a cold. Note also that the newer, nonsedating antihistamines have not been shown to be of any benefit whatsoever for treating the common cold. That provides additional proof that any benefit of antihistamines for cold symptoms is simply a result of their sedating properties.
*these Cochrane Reviews are about as good as it gets in terms of locating, appraising, and distilling the evidence for topics in clinical medicine.
What about this
More discussion here
Antihistamines are downers and decongestants are uppers.