View photos of the medicinal plant Eschscholzia californica ssp. mexicana (Mexican poppy), profiled in Medicinal Plants of the American Southwest.

A passage from Medicinal Plants of the American Southwest:

Consider California poppy (Mexican poppy) a sub–opiate, meaning its effect is broadly opiate–like, though much weaker than medically used pharmaceuticals. Use the plant when sleep is difficult from anxiousness and physical discomfort. It is mildly lessening to both nerve centered and muscular pain.