Is it okay for me to take milk thistle even though i am allergic to ragweed?

Good question!: Both milk thistle and ragweed are in the asteraceae botanical family. While this might be enough to increase the chance they share common allergens, i was unable to find information in the scientific literature that the allergy to one increased risk to the other. Since information is lacking, be cautious and use the expertise of an allergist. A skin test might be helpful or a stepwise challenge.