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Pharmacy/false positive


Can Cephalexin 500 Mg Cap Su and Smz/Tmp Ds 800-160 Tab A combined with ibuprofen cause a false positive for THC  my fiance was tested at work and came back positive for THC and he DOES NOT smoke marijuana Please help him keep his job that he so loves and is very good at  thank you

Dear Kelley

None of these should cause a false positive for THC. If it was the quick test that was used they very often show false positives and should be followed by a more precise test for verification. However, I will say that, especially in the US there appears to be many laboratories doing these tests which produce many false positives. When a test is done the person involved should always have a sealed second specimen provided in case of dispute which can then be tested by a reputable laboratory.


Alan Galbraith


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Dr Alan Galbraith


I can answer most questions on most drugs. Answers can be given in either technical or layperson terminology. My main areas of interest are psychiatric, gastrointestinal and cardiovascular drugs.


I have been a university lecturer/head of department for almost thirty years, but am now retired. My research interests were alcohol, smoking and cardiovascular disease.

Institute of Biology, London.

Author of "Fundamentals of Pharmacology" 5th Edition published in November 2007 by Pearson Education, Australia.

BSc(Hons);MSc;PhD;MIBiol; Cert Biol; HECert

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