I'm not sure when the use of poppy for the relief of pain was made illegal for herbalists, but it certainly is. In fact, in California one can be cited and made to uproot and discard any poppy plants that are even remotely suspected as being used for medicinal purposes. It is certainly clear why this is the case; the latex of the poppy plant has a long history of addictive abuse both in China and later in its extracted and refined form today as morphine and heroin.
However, herbalists are finding other members of the Papaveraceae family to have similarly powerful analgesic pain-relieving properties. Even California poppy, today one of the most popular herbs sold for insomnia in Europe, has somnolescent and mild analgesic properties.
Recently, a study appearing in the January 20,2014 issue of Current Biology and conducted by a team of researchers together with Chinese herbal practitioners at the University of Irvine in California found yet another member of the Papaveraceae family, Corydalis yanhusuo, to also be an effective non-addictive analgesic for both acute inflammatory and nerve pain. (Image of Corydalis yanhusuo at right from http://www.itmonline.org/arts/pain.htm)
Tests were done on rodents who had induced inflammatory pain associated with tissue damage and infiltration of immune cells, and injury-induced neuropathic pain. The latter is particularly important because evidently Western medicine has no adequate treatments for neuropathic pain. This makes corydalis at least the second and arguably the most powerful herb one can use for the treatment of pain (the other herb commonly used by Western herbalists for nerve pain is St. John's wort, or Hypericum perfoliatum).
The teams screened 10 traditional Chinese medicines known as analgesics and nearly 500 compounds known for their pain-relieving abilities. Only dehydrocorybulbine (DHCB), the constituent found in Corydalis yanhusuo, produced a reproducible effect. Unlike poppy and its biochemical derivatives, DHCB does not necessitate the raising of doses with its subsequent addiction as do other conventional pain relievers. This is the first time that the coordinated efforts of both Chinese medical doctors and researchers East and West have been able to extract, identify and test a specific biochemical constituent that seems largely responsible for the remarkable analgesic properties of this medicinal herb.
These are several species of corydalis throughout the world, and indeed many of these may have the same or even greater analgesic properties, but the one most used in Traditional Chinese Medicine (TCM) for thousands of years grows in Siberia, Northern China and Japan. Corydalis yanhusuo is one of the herbs most frequently used by Chinese herbalists for the treatment of pain and various other circulatory problems. As such, it is also used for the treatment of cancer and coronary heart disease. It is classified as a powerful Blood-moving herb, which relieves the stasis that causes pain according to TCM theory. The root is administered in 4.5 to 9 grams per dose in a divided decoction, taken twice daily to alleviate menstrual cramps, chest pain and abdominal pain. According to Olivier Civelli, chief researcher at UCSC Irvine, more than 50 million Americans are affected by neuropathic pain, for which DCBH could be of great benefit. These people could receive the relief they need through this powerful herb.
As an aside, marijuana-infused oil or ointment (made with lard) is a traditional Central American folk use of the herb for the relief of arthritis, sprains and other aches and pains. Increasingly with the legalization of marijuana in some states, its use for pain has been widely acclaimed as medicine-makers produce their novel pain-killing marijuana ointments and tinctures. But remember, herbal formulas are usually (though not always) more effective than single herbs. A good formulation would be a combination of cannabis with corydalis.
Currently, Corydalis yanhusuo extract is one of the primary ingredients in Planetary Herbal's Willow Aid. Plants and seeds are also available from various online sources.