By MATTHEW PERRONE, AP Health WriterWASHINGTON (AP) — An experimental medication made from marijuana successfully reduced back pain in a new study, offering further support for the drug’s potential in treating one of the most common forms of chronic pain. Health officials in Canada and Europe have previously approved a pharmaceutical-grade form of cannabis for several types of pain, including nerve pain due to multiple sclerosis. Chronic pain is one of the most frequently cited conditions of people enrolled in state-run medical marijuana programs. For the new study, patients with back pain were randomly assigned to take Vertanical’s proprietary liquid cannabis extract or a placebo. In the U.S., the company says it is “working closely” with regulators to design a study to support FDA approval.