Former RKL (RICH KIDS ON LSD) vocalist Jason Sears passed away on Tuesday (Jan. 31) in Tijuana, Mexico while receiving treatment at an alternative detox clinic that primarily serves U.S. citizens struggling with drug addictions, according to the San Diego Union-Tribune. He was 38 years old.The cause of death was pulmonary thrombosis, according to an autopsy report. State authorities weren't planning on filing charges because Jason Sears appeared to have died of natural causes due to other health problems, a spokesman with the State Attorney General's Office said, according to the San Diego Union-Tribune. Sears was one of several U.S. patients at a Tijuana clinic, according to a city police report. The clinic — which is operated through a U.S.-based group — occupies a two-story house in a quiet Tijuana neighborhood near the beach. It has no obvious name or signs. The clinic is operated through the Ibogaine Association, which displays a picture of the house on its Web site and provides a San Diego phone number — though a staff member reached there declined to comment on the death or provide additional information on how the program is run. Ibogaine is a drug derived from a West African plant that can help overcome addiction and eliminate withdrawal, according to some animal research and limited case studies in humans. But the drug can also induce powerful hallucinations, and that, along with animal studies that indicate potentially dangerous side effects, have made U.S. regulators reluctant to endorse human clinical studies. It is illegal to use the drug in the United States. The attending physician at the Tijuana clinic, Itzcoatl Medina, said Sears was receiving treatment when he died. Medina said a pulmonary thrombosis is an obstruction in the vascular system, usually from a blood clot. Medina said that infections can sometimes lead to clots, and Sears had refused to take antibiotics for an infection. Medina, who declined to comment on who runs the clinic, said Sears had signed a release form to participate in the program. According to PunkNews.org, RKL was a fixture of the '90s Santa Barbara punk scene. Two members of the band, guitarist Chris Rest and drummer Dave Raun, went on to join LAGWAGON. Sears was the vocalist of the band in 1983-1989 and 1994-1996 and was responsible for the vocals on the band's Epitaph full-length "Riches to Rags". The band split up around 1996 but had reunited in various configurations 2001, 2002, 2004 and 2005. A posthumous collection, "Keep Laughing - The Best Of RKL", appeared in 2001. After his time in RKL, Jason recorded "Jason Sears And Mercury Legion", which was released last year. Jason also sang on "Strait Up" a tribute to the late James Lynn Strait of SNOT on "Until We Meet Again".