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View Full Version : Can second hand smoke cause a false positive for THC?


celtic250
Jul 31, 2012, 10:21 AM
I will be going to some concerts here in the next few weeks in which people will be smoking marijuana. These concerts are indoors and I have a drug test for a job I got when I arrive home. I was wondering if it is possible to test positive for THC from the second hand smoke? Thanks and I look forward to hearing back from the professionals!

DrBill100
Jul 31, 2012, 10:43 AM
I will be going to some concerts here in the next few weeks in which people will be smoking marijuana. These concerts are indoors and I have a drug test for a job I got when I arrive home. I was wondering if it is possible to test positive for THC from the second hand smoke? Thanks and I look forward to hearing back from the professionals!

It is quite possible whether the test is urine or hair based although hair test is by far the most likely candidate. See references below.

For urine and blood test after passive smoke exposure to marijuana a recent study conducted in Denmark offers the most definitive information available to date:

THC in blood and urine after passive exposure in coffee shop (http://www.ncbi.nlm.nih.gov/pubmed/20465865) J Anal Toxicol. 2010;34(4):196-203.


For hair contamination see:

Substance Abuse and Mental Health Services Administration. (2012) (http://kap.samhsa.gov/products/manuals/pdfs/TAP32.pdf). Clinical drug testing in primary care. Technical Assistance Publication (TAP) 32. HHS Publication No. SMA 12-4668. Rockville, MD: Substance Abuse and Mental Health Services Administration. http://kap.samhsa.gov/products/manuals/pdfs/TAP32.pdf

Volker Auwärter, Ariane Wohlfarth, et al (2010) Hair analysis for Δ9-tetrahydrocannabinolic acid A—New insights into the mechanism of drug incorporation of cannabinoids into hair (http://www.citeulike.org/user/DrBill100/article/6817395). Forensic Science International, Vol. 196, No. 1-3. (20 March 2010), pp. 10-13

celtic250
Jul 31, 2012, 11:17 AM
So if my understanding is correct from that study, the samples were taken in intervals after the contact with smoke and none tested positive after 6h? I will be taking this test ~24h after the last concert. I noticed that it was conducted with people who were in a coffee shop and doubt I will be as exposed as them as well as in a much larger area. From my understandings I should be perfectly fine at that time when taking a urine analysis?