Re: what causes the green glow of cannabis under a 'black light'

Anthony,
Most drugs absorb ultraviolet light and this is one of the test that I 
perform when analyzing drugs.  For example what I do is put a really small 
amount of suspected cocaine in a weak acid and place it into a UV 
Spectrophotometer and the drug will absorb some of the UV light and then 
the computer prints off a spectrum (graph).  Now if you were to place a 
piece of blotter paper containing LSD into some alcohol and then put it 
under the UV light it would fluoresce (glow), if there were no LSD on the 
blotter paper the alcohol solution would look clear.  

I have never (nor has my collegues) heard of the technique you mentioned 
about shining a black light (UV light) on a person suspected of using 
Marijuana.  One of my first questions is have you performed this technique 
on a suspect who glowed but then was proven didn’t smoke MJ?  This would 
be a false positive.  Furthermore, have you shined the light on an officer 
and got negative results?  I’m not aware of how much experimentation you 
have conducted, and would be interested to hear more if you want to 
contact me through email then call me.

It is a  good question so I did some experiments myself.  I took some 
Marijuana and extracted the Cannabinoids with a solvent (which there 61 of 
them THC being the most prominent).  I then put the extraction on my 
fingers and checked them under UV light.  My fingers which contained THC 
glowed the same amount as my other hand that had no THC.  The next thing I 
did was to rub MJ between my fingers until they felt sticky with THC, and 
that also produced what I would say was negative under UV.  So this leads 
me to believe the THC is not causing the glowing you refer to.  Now if you 
eliminated the false positive and the negative results as a source of 
error, then I would look at something else causing your glowing.  My co-
worker who does DNA says saliva might glow under UV, or you might try 
alcohol?  Good luck, be safe.

dkoppenhaver@juno.com