Are you taking supplements? Are you taking prescription medications too? Sometimes the two types of medications inhibit the reactions of each other. Instead of being awesome for you, the medication ends up being bad for you.
Echinacea is a supplement that some may use to help enhance their immunity when cold season hits. Often, those with cold symptoms will take one Echinacea a day to run off a cold. This is a great herb for those characters who have been out in the weather or just can’t seem to enhance their health. Dungeon Masters may want to give out experience points to those who find this pink cone flower blooming alongside the road, harvest, and dry it for later use. While boosting the immunity for the character, there is also a change for an allergic reaction similar to penicillin, therefore the DM needs to roll a check for this. If there are any other potions in play, again, another check needs to be done to see if the herb has enhanced or decreased the effects. Oh, what fun this could be?