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Why does post-mortem result show positive for Marijuana?

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Addiction Medicine Specialist
Practicing since : 2002
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An accident victim had a pre-mortem blood and/or urine drug screen that was negative. Post-mortem vitreous fluid was supposedly positive for marijuana. Is this possible? I was told that marijuana "lasted longer in vitreous fluid" . Considering Marijuana being hydrophobic and vitreous fluid being primarily water, this does not make sense to me. Thank you.
Posted Fri, 7 Mar 2014 in Smoking and Alcohol Addiction
Answered by Dr. Preeti Parakh 1 hour later
Brief Answer: Explained below. Detailed Answer: Hi, Welcome to Healthcare Magic! Yes, you are right in saying that vitreous humor is primarily water and the metabolites of marijuana are hydrophobic. In fact, this is the reason why in post-mortem specimens, the highest amount of 11-Nor-9-carboxy-delta9-tetrahydrocannabinol (THC-COOH) are found in bile and the least in vitreous humor, with urine and heart blood coming in between. I cannot explain the paradox in the ante-mortem and post-mortem results. The only possible explanations are: 1) The person consumed marijuana after the drug test and before meeting with the accident. 2) The ante-mortem drug test was wrong. 3) The post-mortem drug test was wrong. The only other point that may have a bearing is that the usual drug screens are conducted using dip stick tests which are less reliable than other methods like GC-MS (gas chromatography mass spectroscopy). If the vitreous humor was tested using reliable methods like GC-MS, it may have picked up traces of cannabis which may have been missed by previously conducted tests. Best wishes. Dr Preeti Parakh MD Psychiatry
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