ASA has successfully intervened in a civil lawsuit that the County of San Diego filed against the California Department of Health Services (DHS) on February 1, 2006 in San Diego Superior Court. Jointly with the ACLU Drug Reform Law Project (DLRP), Drug Policy Alliance (DPA), and representing five patients, a physician, and the Wo/Men's Alliance for Medical Marijuana (WAMM), ASA fought on behalf of the rights of patients across the state. Specifically, ASA argued that federal law does not preempt state law, and that the County of San Diego must abide by the Compassionate Use Act and SB 420.

San Diego County Supervisors claim to have filed the lawsuit in response to a lawsuit threatened by San Diego NORML over the County's objection to implementing the state's medical marijuana ID card program. Therefore, the case is called San Diego County v. San Diego NORML. On July 7, 2006, ASA, DLRP, and DPA filed a motion to intervene, which was granted on August 4. Then, on September 1, the parties filed their motion for summary judgment on the pleadings. Attorneys for ASA and the ACLU argued the case in San Diego Superior Court on November 16, 2006, and secured a tremendous victory for patients in California. On December 6, 2006, Judge William R. Nevitt Jr. confirmed the validity of California medical marijuana law by ruling on the side of patients and rejecting the counties’ challenge. Despite a ruling clearly showing that federal law does not preempt state law, the County of San Diego appealed the Superior Court decision on February 22, 2007. ASA will continue to fight this lawsuit and is confident that patients will ultimately prevail and that San Diego will be forced to abide by and implement California's medical marijuana law.

The intervening defendants included Wendy Christakes, Pamela Sakuda (now deceased), William Britt and Yvonne Westbrook, Californians who use physician-recommended marijuana to treat medical conditions and their side-effects, including chronic pain and sciatica, multiple sclerosis, rectal cancer, epilepsy and post-polio syndrome. Also represented was Sakuda’s spouse and caregiver, Norbert Litzinger, and Dr. Stephen O’Brien, a physician who specializes in HIV/AIDS treatment in Oakland, California, and believes that many of his seriously ill patients benefit from the medical use of marijuana. In addition to being co-counsel, ASA was also an intervening defendant on behalf of our membership, with over 30,000 medical marijuana patients, caregivers and physicians residing in California. WAMM, another intervening defendant is a medical marijuana collective and hospice located in Santa Cruz, California, whose 250 members, the majority of whom are terminally ill, use marijuana to treat a range of conditions.

The Counties of San Diego and San Bernardino have appealed the superior court ruling to the Court of Appeals for the Fourth Appellate District.The County of Merced, by contrast, did not appeal the ruling and, instead, has implemented the identification card program.

On July 31, 2008, the Court of Appeal for the Fourth Appellate District, Division One issued a published decision denying the Counties' position. On October 16, 2008, the California Supreme Court denied the Counties' Petition for Review and the United States Supreme Court denied the Counties' cert. petition on May 26, 2009, rendering the case final for all purposes.