Chemist’s perspective on hair tests (psychemedics, passed)


Hi. I’m a recent college graduate who has recently survived a run in with a psychemedics pre-employment hair follicle drug test (HFDT). I have brown hair and I smoked five or six light uses (three-four hits) in the "three month" period being tested. Also they used chest hair because my head was too short.

I probably had no reason to worry, but because I have a degree in chemistry and my little scare drove me to a borderline-obsession with HFDTs I wanted to share what I’ve learned, and try to use my chemistry background to try and shed some light on some of the conceptions and misconceptions surrounding HFDTs. Hopefully this helps.


To begin, I should probably cover what a HFDT is. HFDTs seek to detect the metabolite of THC and they work by taking a sample of hair, washing it in a solvent such as methanol, and then dissolving it in another solvent. I couldn’t find a great deal of information about the processing of the hair because of its proprietary nature. After the hair, and the drugs within the hair are dissolved, much like salt cubes dissolve in Water, the solution undergoes an immunoassay.

An immunoassay is essentially where a signal molecule is introduced to the hair/drug solution that binds specifically to the drug or metabolite. Like a lock and key, the THC bonds with the signal molecule. Upon binding to the THC, the molecules undergoes a change where it can be detected by an instrument. A common method is to use molecules that fluoresce, or give off light, after binding. Therefore a very sensitive light detector can determine how much drug is there. I’m not sure if this is the exact method used but it’s close enough. If you fail the immunoassay (usually 1 pg/mg of hair or 1 part per billion), your hair is run through a GC/MS. That stands for gas chromatography/mass spectrometry.

Gas chromatography is a separation technique where the hair/drug solution is injected into a column with gas flowing through it. The column is usually coated with a solid or liquid "adsorbent." Based on the different attractions of the molecules in the hair/drug solution to either the gas or the adsorbent column, the different molecules will come out at different times. In other words, if all things are the same, the THC metabolite (TCH-COOH) will come out of the column at about the same time, therefore allowing it to be isolated from everything else in the solution. The isolated THC-COOH then enters the mass spectrometer. The MS then splits the molecules coming out at that time into smaller fragment molecules. Based on the pattern of fragments produced they can say whether drugs were incorporated into the hair.


I guess that leads us into the question of how the THC-COOH they’re looking for gets incorporated into the hair in the first place. When you smoke the molecules in the smoke enter the lungs in gaseous form and are then dissolved in the blood flowing around the lungs. The body then essentially changes the THC molecules into the metabolite THC-COOH which inhibits it’s psychoactive effects. Because both forms of THC are lipophilic (attracted to fats) they take a while for the body to remove completely. Because the drugs can potentially be incorporated into the hair for as long as it’s in the blood, this sounds like bad news. But because hair has very little to no fat content, it’s really not that bad of news for those who have to take an HFDT. Hair is mainly protein (the same keratin protein as fingernails) so THC-COOH is very weakly incorporated into the hair. The exact mechanism for incorporation hasn’t been adequately researched, but mention of melanin (the molecule that gives hair it’s color) comes up somewhat frequently. This idea that THC-COOH is incorporated into hair through melanin is most likely the reasoning behind bleaching hair to beat the test, and also the idea that dark hair absorbs more metabolites. Neither of these have been confirmed through scientific testing, however.


On that note I just wanna talk about some miscellaneous ideas and findings. First there’s a very interesting study I found. Hopefully I can post this link here. ((only registered users can se the link, login or register))
The study tested 53 daily or regular users of marijuana for TCH-COOH in hair using GC/MS. Of the 20 daily users only 16 had levels of TCH-COOH above the detection limits of the GC/MS (.1 pg/mg). Of the 33 non-daily users (1-5 times a week) only 16 had those levels of TCH-COOH.

I also want to comment on the bleaching of hair. If melanin were the molecule to which the metabolites were bound to, bleaching hair may affect drug levels. Because bleaching hair obviously does penetrate the matrix of the hair enough to oxidize the melanin (why your hair turns white when bleached) it seems to disprove the idea that the hair matrix is impenetrable. On that note though, when they say bleaching they mean by an oxidizing agent. Hydrogen peroxide (H2O2) will work just fine. People putting concentrated bleach (NaOCl) on their heads are causing unnecessary damage. It’s not the strong base that does it. STOP BURNING YOUR HEADS WITH STRONG BASES PEOPLE! There is some evidence that a base increase penetration of the hair as seen by the practice of adding a small amount of ammonia to bleaches and dyes by professional hairdressers. A thirty to one peroxide/bleach mixture should be enough. I’m not sure how much ammonia is used by professionals but please people use caution not to burn your head. Also I did not see the reasoning in multiple re-dying of the hair. Maybe multiple peroxide washes but other than that I don’t see why. I could be missing something there though.

Also, a google for DrBill or JerryG might be very comforting for some of you.


I would just like to end by reiterating that hair tests are not a very good way of detecting even daily use of marijuana. If you have only used a handful of times, especially light use, there’s not much chance you’ll be caught. If you’re a heavy user or you can’t afford to take chances a couples bleaches and a redye may improve your chances. Remember though, peroxide not the strong base cleaning bleach! Good luck and if there’s anyway you can help spread this I hope you do.
Via (only registered users can se the link, login or register)

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