How can "viral infection" be a side effect of a drug?

I saw a TV commercial tonight for Nasonex. At the end they mentioned the side effects of course, and one of them was “chance of viral infection”. Checking on their website confirms this:

Now I’m not a doctor, but I thought only viruses caused viral infections. How is it possible that a prescription drug can cause them too?

That was not supposed to be a cryptic title. Stupid quote bug. It was supposed to be: ‘How can “viral infection” be a side effect of a prescription drug?’

Could a mod fix it please? I’d be eternally grateful.

Reading it carefully, it does not ‘cause’ a viral infection, merely allow one to happen more readily. I’m not sure of its action but in some way such steroids can apparently facilitate action of viruses. Similarly anti-biotics often ‘cause’ (allow) fungal infections because they remove bacteria that compete for the same resources.

Nasonex is a steroid (see my post on the topic of steroid muscle building in GQ (shameless plug)). it reduces inflammation, but also lowers the local tissue’s resistance to infection, by decreasing the immune response to invaders in that area. Viruses (viri?) which would have been de-activated by your extremely immune antibody laden snot are now able to penetrate, as are fungi, and more rarely bacteria. Still, its usually worth the risk if you’ve got chronic nasal congestion blocking you up. That too can encourage nasal and sinus infections, by keeping your passages bottled up with all that oligosaccharide rich mucus.

Qadgop, MD