Corydalis Formula is a combination of the classical Peony and Licorice Formula with corydalis (yan hu suo).  Peony and Licorice Formula is traditionally used for pain, cramping, or muscle spasms caused by injury for the liver blood or yin.  Corydalis is used for pain from stagnation of qi and blood.  These herbs together make this a suitable formula for many types of pain, muscle spasms, and cramps.