Why Eric positive drug screen on CSI Miami?
He wasn't positive for doing drugs himself. He was positive for having drugs in his system. Later in that episode they explain how he was sitting with his sister while she was smoking the Mary j.
Yes he only failed the THC in the blood/or urine test but not the more stringent hair follicle test that shows a history of chemicals in your system based on patterns of growth in hair shafts.
Yes. DXM is slightly related to opiates but not close enough to cause a positive drug screen. It is very unlikely for one drug to cause a false positive on a drug screen for any other substance. Drug screens test for metabolites of specific drugs. All drug tests have a rating based on specificity and sensitivity. The higher the sensitivity, the lower the specificity. Basically it is only possible to have a false positive by…