CWeak evidence, or evidence againstBotanical
The short answer
Trials are inconsistent and the preparations differ so much that they are barely comparable. Not a reason to skip the things that do work.
Who this is actually for
No group with an established need.
What it is legally allowed to claim
Nothing. There is no authorised EU health claim for this substance, so any packet promising a specific benefit is making a claim it is not entitled to make. That is worth knowing before you judge the price.
How much is too much
No upper level.
Cautions and interactions
No authorised EU health claim. Avoid in autoimmune disease and with immunosuppressants. Allergic reactions occur, particularly in people allergic to daisies and ragweed.
Ask a pharmacist before you start anything. Interactions with prescribed medicines are the most common way supplements cause harm, and they are easy to check. Bring the actual packet, or a photo of the ingredients panel, because doses and forms vary enormously between products. Nothing here is a substitute for advice about your own situation.