well, anything that will treat an upper respertory infection in humans (a cold) will be safe for a rat.
i already give them echinacea regularly, just to keep their immune systems strong.
a few days ago, one of them (Pocky) was making a really horrible snoring sound when he breathed hard (i picked him up and he got a little scared and started breathing fast) he sounded so congested. so i made up a brew with peppermint, chamomile, cinnamon, lavender and echinacea. i put it right by their cage as it cooled so they could breathe in the vapors, then once it cooled, i put it in their water bottle.
well, by the time the water bottle was empty, about 2 days later, Pocky's breathing sounded normal!
so basically i'm asking, how would you treat a HUMAN upper respertory infection (cold) and i can translate that into a smaller dosage for a rat.