There's two herbs that I know of that are part of the Ragweed Family which are echinacea and chamomile so if you're allergic to Ragweed then you will likely not be able to use those two herbs of echinacea and chamomile.
Also if you're allergic to Ragweed then you might want to avoid the foods Sunflower Seeds, Cucumbers, melons and zucchini as those foods are all part of the Ragweed family as well.