These are mostly just theories, so we can use the common RE healing items in a narrative way in the RP. Feel free to counter any of the points, tell me what you'd like to see used, any discrepancies, etc.
It's usually widely accepted that the green herbs are ingested (as in eaten) and they act as a natural blood coagulant. In gameplay terms, that would mean that it helps clot blood from major wounds and maybe act as a temporary painkiller until the character got to safety, thus "reducing" damage taken or allowing them to ignore it (within reason, of course) until they could seek proper medical attention.
Blue herbs heal poison--they aren't magical and don't immediately show effects, but they probably contain a ridiculous amount of antioxidants and naturally-occuring antibodies that encourages the body to flush out toxins faster through mucus, blood, saliva, etc. thus resulting in the poison being ejected from the infected character a lot faster than it would have been normally through bodily secretions including sweat.
Red herbs don't do anything on their own (except maybe add some nice garnish to salads) but the enhance what other herbs do when mixed.
F. Aid Spray is much the same--it helps speed up metabolic rate and encourages cells to knit together faster, while killing bacteria and acting as a "liquid bandage" of sorts. But the downside is with the increased metabolic rate the patient experiences extreme hunger and fatigue faster... which would make sense, considering Umbrella makes F. Aid Spray as well as... other things. It's almost like a small, beneficial touch of the T-Virus, but not enough to infect you. It would be handy to have a stock of food available, though not neccessary, though excessive use would make for discomfort and performing at less than physical peak, and probably would lead to loss of conciousness. This is probably why it's a lot less widely available than green herbs.
Hemeostatic supplement tablets do exactly as the name says--they clot blood. Quickly.
However, they don't have the same "healing" effect as green herbs do--your character will simply stop bleeding, but will remain injured, without the "painkiller" effect.
Anti-Virus pills are pretty self-explanatory, as well. They are a three-dose blister package of white tablets with a black stripe up the center which need to be taken seperately over the course of an hour's time. Each tablet is a condensed dosage of a special antibody strain that "eats" the T-Virus--these would naturally not be just laying around, so it seems more plausible that Umbrella would have included this strain unknowingly into some of their other pharmaceutical products with no knowledge of how it would have effected the T-Virus in living organisms. It seems like a stroke of luck for PCs that are desperate enough to take maximum strength Ibuprofin-based pills for headaches brought on in the first stages of the T-Virus, but it's anybody's guess what medicines have the anti-virus in them.