Addison DeMoura, left, and David Lampach, both former marijuana growers, founded the Steep Hill Lab in 2008. The Oakland facility has tested 12,000 pot samples.OAKLAND The mere existence of the Steep Hill Lab presents a pointed question: How safe is the marijuana provided to hundreds of thousands of medical pot users in California? How safe is the marijuana provided to hundreds of thousands of medical pot users in California? The Oakland laboratory, started in 2008 by two former growers, has tested 12,000 pot samples to assure marijuana businesses that their product isn't tainted by dangerous toxic molds or pesticides. Nearly 50 medical marijuana dispensaries and pot-growing networks contract with the lab, California's most renowned cannabis testing location. Tens of thousands of dollars in medical marijuana can be rendered useless if samples are found to contain toxins that could trigger respiratory infections, sinusitis or worse. There is no Food and Drug Administration for marijuana.