Pacific willow (Salix lucida ssp. lasiandra) has been used traditionally by various Indigenous peoples of North America as a remedy for pain, including backache. The historical use of willow bark for pain relief dates back thousands of years, and it is well documented that different willow species, including Pacific willow, were used in decoctions or poultices to alleviate various aches and pains. This traditional use is grounded in the presence of salicylates in willow bark, which are precursors to acetylsalicylic acid (aspirin), a known analgesic and anti-inflammatory compound.

While there is strong scientific evidence supporting the pain-relieving properties of salicylate-containing willow bark in general, most modern research has focused on European species such as Salix alba (white willow). There is a lack of high-quality clinical trials specifically investigating Pacific willow for backache. However, given the shared chemistry among willow species, it is plausible that Pacific willow may exert similar effects. Thus, its use for backache is primarily justified by ethnobotanical tradition, with indirect scientific plausibility based on related species. The strength of evidence for Pacific willow specifically is moderate from a traditional perspective, but weak from a direct scientific validation standpoint.