Peony is a plant. The root and, less commonly, the flower and seed are used to make medicine. Peony is sometimes called red peony and white peony. This symptom, particularly if it occurs with a dry cough or little or no exertion, could signal a potentially serious problem, including a pulmonary embolism (blood clot in the lung) or interstitial lung disease (scarring of the lung tissue), which occurs in as many as one in 10 people with RA. If you are taking methotrexate, another possible cause is methotrexate pneumonitis (also known as.