I’ve read that elderberry, as with other herbal immunity boosters, can interact with immunosuppressive medications. If you are on a DMARD, this may be true. As I’m on immunosuppressive meds, I no longer use elderberry or other herbal immunity builders.

However, WebMD has this:

“Autoimmune diseases" such as multiple sclerosis (MS), lupus (systemic lupus erythematosus, SLE), rheumatoid arthritis (RA), or other conditions: Elderberry might cause the immune system to become more active, and this could increase the symptoms of autoimmune diseases. If you have one of these conditions, it's best to avoid using elderberry.”

So, best to check with your physician.