Are Hair Follicle Tests Accurate For Detecting Cannabis Consumption?


Recent research has called into question whether hair follicle tests are actually accurate measurements of cannabis consumption.

Anna Wilcox
Feb 7, 2017
Hair Follicle Tests Accurate
Photo credit

Hoping to pass a hair follicle test? Obsessively washing your hair, avoiding cannabis smoke and cannabis products, and making sure the rest of you is squeaky clean may be your best options. Recent research has called into question whether hair follicle tests are actually accurate measurements of cannabis consumption. Yet, while scientists duke it out, thousands are hair tested every day.

What do hair follicle tests look for?

Hair Follicle Test 1 Are Hair Follicle Tests Accurate For Detecting Cannabis Consumption?
Photo credit

Hair follicle tests are a common way to test for the habitual use of drugs and medications. This test is especially effective when searching for amphetamines, cocaine, opiates, which leave urine and blood stream very quickly.

The most common hair test looks for residual metabolites from different substances. Different testing labs may look for different things depending on what was ordered.

Commonly tested substances include:

Are hair follicle tests accurate?

Hair Follicle Test 2 Are Hair Follicle Tests Accurate For Detecting Cannabis Consumption?
Photo credit

In 2015, German forensic researchers called the accuracy of the hair follicle drug test into question. In two small studies, the team treated two participants with tetrahydrocannabinol (THC), the primary psychoactive in cannabis, and one participant with THCA, a nonpsychoactive precursor to THC.

Those receiving THC were given 2.5 milligrams of dronabinol, a synthetic THC, three times a day for 30 days. Researchers then tested a sample of new hair growth for THC-COOH, a THC metabolite.

When you inhale or ingest cannabis, the body breaks down THC into various metabolites. One of those metabolites is called 11-nor-9-hydroxy-THC (THC-COOH).

The long-standing theory has been that THC-COOH travels through the bloodstream and eventually makes its way into the hair. However, this new research suggests that may not be the case.

Hair follicle analyses are supposed to search for the presence of this metabolite to indicate whether or not a person has been consuming and metabolizing cannabis on a regular basis. Surprisingly, the researchers didn’t find much THC-COOH in their samples.

They then tested segments of older hair, from a time when the participant had not consumed cannabis. Interestingly, the participants tested positive for THC in older samples. The verdict? THC on hair must be coming from external sources, rather than circulating through the bloodstream.

To reach THC concentrations of 50 pg/mg (cut-off recommended by the Society of Hair Testing21) through incorporation via the bloodstream would require consumption of extremely high amounts of THC, which would certainly be associated with a several-fold higher amount of THC incorporated through contamination routes (cannabis smoke exposition and/or transfer by contaminated fingers).

Simply said, for THC to enter the hair through the bloodstream, a person would have to consume extremely high amounts of the stuff. Though, individuals who consume the herb regularly are more likely to be exposed to the compound from external sources, causing more of it to end up on your hair.

Thus, the researchers conclude that THC concentrations in hair are not accurate measurements of use. They state,

Consequently, THC findings in hair cannot be regarded as a proof of cannabis consumption.

Unfortunately, this study comes with a few caveats. The test included an extremely small sample size, which makes it difficult to determine whether this logic should be applied to all cannabis hair testing.

Further, chronic, long-term cannabis consumers may be more likely to have higher concentrations of THC metabolites in their hair.

So, how does cannabis end up in the hair?

THC COOH Are Hair Follicle Tests Accurate For Detecting Cannabis Consumption?
Photo credit

Based on the new research, THC-COOH ends up in hair in two primary ways. First, it travels through the sebaceous gland, the gland that secretes natural oils on the skin and scalp. This natural oil is also known as sebum. THC-COOH is then secreted in your body’s natural oils along with sweat, which coats strains of hair.

THC and other cannabis compounds can also end up on the hair of non-consumers. The cannabinoids wind up on hair through interaction with the cannabis plant and the people who consume the herb. Cannabinoids can be transferred via the sebum, as well as in smoke, sweat, and hand-to-hand contact.

While consumers still need to be wary of possible bloodstream transfer as well, the German research perhaps gives credence to why many successfully pass hair follicle tests after intensive topical detoxification. Washing the crap out of your hair may be the best bet for passing a hair follicle test, though things are still risky.

How long do you have to be clean to pass a hair follicle test?

test2 Are Hair Follicle Tests Accurate For Detecting Cannabis Consumption?
Photo credit

To pass a hair follicle test you have to be clean for a total of 90 days. Though, follow-up studies to the German research will perhaps one day clarify if this is, in fact, accurate. This is true for all substances, including cannabis.

This is because of the way the hair is tested. Hair samples are cut as close to the scalp as possible, where new growth occurs. The clipping is around 1.5 inches (3.8 centimeters) long, which represents about 90 days of hair growth.

90 days is not an exact number. The hair follicle test comes with some variability. Rates of hair growth are different in everyone. What is 90 days for one person could be 111 in another. The rate of hair growth also depends on age. The older you are, the slower your hair will grow.

A healthy hair growth rate is a half inch (1.25 centimeters) per month. If your hair is in poor health or your hair is otherwise slow-growing, you may need to stay clean longer to pass a hair follicle test.

For more information on drug testing, check out the full article here

Anna Wilcox
Feb 7, 2017