View photos of the medicinal plant Populus tremuloides (Aspen), profiled in Medicinal Plants of the Western Mountain States.

A passage from Medicinal Plants of the Western Mountain States:

Prosaic in application, Aspen symptomatically addresses painful conditions. The tree’s bark has the greatest aspirin–like/antiinflammatory effect (the leaves can be used as a half–strength preparation). Drink the tea for issues ranging from arthritic flare–ups to acute injuries. Even the diffuse tissue and muscular pains of fibromyalgia are often quieted. Essentially, if it hurts, a cup or two of Aspen tea may not cure, but it will ease.