I feel like your question is two-dimensional. First, I think you're wanting to know if being unwell can make a substance less potent. Of course, the answer is that there are too many different conditions to make an objective statement in that regard. If you are talking about influenzal. common cold, sinus infections etc. the answer is no. These conditions do not directly impact the way drugs are metabolized., as far as I know at least. If anyone knows anything, please chime in.
Now, more on the practical side: insufflation in an imperfect environment
This is pretty easy to understand. When you insufflate/sniff/snort dry, powdered material it is going to come into contact with the nasal mucosa and "stick" to the walls of your sinus. The next step is the powder and mucous forming a solution. Osmosis allows the blood vessels lining the walls of your sinuses to then absorb this solution directly into your blood stream.
So, being sick isn't the issue per se. Issues arise when the sinuses are in a state that interferes with this process. A healthy person with a normal functioning sinus system has the ideal conditions for this process. You only want enough moisture. If you have too much mucous in your sinuses, your drugs are liable to be taken up by the mucous and swallowed.
It's not a nightmare scenario for you to end up swallowing some of your drugs, just a bit disappointing. Likewise., if the environment is too dry, you can end up inhaling the drugs, bypassing the mucosa completely and again, swallowing the drugs.
This situation is pretty easy to remedy though.
If you are too dry/irritated, go to the store and get yourself a little bottle of saline with the tip for nasal use. Take the top off and add just a bit of baby oil. Blow your nose gently then administer your saline/baby oil mixture in each nostril. Orient yourself however you need to so it doesn't all immediately get swallowed.
Give it 10 minutes for the oil sink in a bit. Insufflate your drugs. After 45-60 minutes, go back and flush each sinus again to remove debris and prevent irritation. Can be repeated if necessary, within reason.
If they are too moist, blow your nose, flush with saline, insufflate drugs shortly thereafter. Just be sure your sinuses aren't inundated with mucous and you will be fine. The practice of flushing your sinuses with saline following insufflation is just a good habit for everyone anyway.
