How much THC must be present to register on a drug test?
Drug tests screen for THC or one of its main metabolites, THC-COOH.
According to Mayo Clinic Proceedings from 2017, federal workplace drug testing cut-off values were established to avoid the possibility that trace amounts of THC or THC-COOH would trigger a positive test.
In other words, passing a drug test doesn’t mean that there isn’t any THC or THC-COOH present in your system.
Instead, a negative drug test indicates that the amount of THC or THC-COOH is below the cut-off value.
Different testing methods have different cut-off values and detection windows, as listed below.
Urine
Urine testing for cannabis is common, especially in the workplace.
In urine, THC-COOH must be present at a concentration of 50 nanograms per milliliterTrusted Source (ng/mL) to trigger a positive test. (A nanogram is approximately one-billionth of a gram.)
Detection windows vary a lot according to dose and frequency of use. In general, THC metabolites are detectable in urine for approximately 3 to 15 days after use.
But heavier, more frequent cannabis use can lead to longer detection windows — more than 30 days, in some cases.
Blood
Blood tests are far less common than urine tests for drug screening, so they’re unlikely to be used for workplace testing. This is because THC is quickly eliminated from the bloodstream.
It’s only detectable in plasma for up to five hours, though THC metabolites are detectable for up to seven days.
Blood tests are most often used to indicate current impairment, for instance, in cases of driving under the influence.
In states where cannabis is legal, a THC blood concentration of 1, 2, or 5 ng/mL suggests impairment. Other states have zero-tolerance policies.
Saliva
Currently, saliva testing isn’t common, and there are no established cut-off limits for detecting THC in saliva.
A set of 2017 recommendationsTrusted Source published in the Journal of Medical Toxicology suggest a cut-off value of 4 ng/mL.
THC is detectable in oral fluids for around 72 hours, but may be detectable for much longer with chronic, heavy use.
Hair
Hair testing isn’t common, and there are currently no established cut-off limits for THC metabolites in hair.
Private industry cut-offs include 1 picogram per milligram (pg/mg) of THC-COOH. (A picogram is about one-trillionth of a gram.)
THC metabolites are detectable in hair for up to 90 days.
Why else might CBD use result in a positive test result for THC?
There are several potential reasons why CBD use might lead to a positive drug test result.
Cross-contamination
There is potential for cross-contamination during the CBD manufacturing process, even when THC is present only in trace amounts.
Cross-contamination may be more likely for manufacturers preparing products that contain CBD only, THC only, or a combination of the two.
The same is true in stores and at home. If CBD oil is around other substances that contain THC, cross-contamination is always a possibility.
Secondhand exposure to THC
Although it’s unlikely that you’ll receive a positive drug test result after exposure to secondhand marijuana smoke, it’s possible.
Some research suggests that how much THC you absorb through secondhand smoke depends on the potency of the marijuana, as well as the size and ventilation of the area.
Product mislabeling
CBD products aren’t consistently regulated, which means that there typically isn’t a third party testing their actual composition.
A 2017 studyTrusted Source from the Netherlands evaluated the accuracy of the labels provided on 84 CBD-only products purchased online. The researchers detected THC in 18 of the products tested.
This suggests that product mislabeling is fairly common in the industry, although more research needs to be done to confirm if this is also true for American CBD products.
Can CBD turn into THC in the body?
In acidic conditions, CBD can turn into THC.
Some sources speculate that this chemical transformation also occurs in the human stomach, an acidic environment.
In particular, a 2016 in-vitro studyTrusted Source concluded that simulated gastric fluid can transform CBD into THC.
However, a 2017 reviewTrusted Source concluded that in-vitro conditions don’t represent the actual conditions in a human stomach, where a similar transformation doesn’t appear to occur.
The researchers in the 2017 review also pointed out that among the reliable clinical studies available, none have reported side effects of CBD similar to those associated with THC.
How can you make sure that a CBD product doesn’t contain THC?
Some CBD products may be safer than others. If you’re considering using CBD, it’s important to take time to evaluate the products available.
Read the product information
Find out whether the product comes from hemp or marijuana. Next, find out whether the CBD is full-spectrum, broad-spectrum, or pure CBD isolate.
Remember that CBD products that come from marijuana, along with full-spectrum CBD products derived from hemp, are more likely to contain THC.
This information should be very easy to find. If it’s missing from the product description, it might be a sign of a not-so-reliable manufacturer.
Opt for products that list the amount of CBD
It’s a good idea to find out the concentration of CBD per dose.
Remember that it may vary according to whether the product is an oil, tincture, edible, and so on.
In many cases, more concentrated CBD products are more expensive, even though they may appear to be the same size or smaller than other products.
If possible, start with a low-dose product.
Find out where hemp-derived CBD products come from
Hemp quality varies by state. More reputable states, such as Colorado and Oregon, have longstanding hemp industries and rigorous testing guidelines. If information about the hemp isn’t available on the product description, contact the seller.
Do your research
When evaluating the product, you should look for certain terms, such as:
- USDA-certified organic
- CO2-extracted
- solvent-free
- decarboxylated
- pesticide- or herbicide-free
- no additives
- no preservatives
- solvent-free
- lab-tested
However, in many cases it will be difficult to prove that these claims are true. The best way is to look for any available lab test results associated with a given manufacturer.
Avoid products that make health-related claims
Epidiolex, an epilepsy medication, is the only CBD-based product with FDA approval. Epidiolex is only available by prescription.
Other CBD products haven’t undergone FDA testing to assess their safety and effectiveness in treating specific health problems, such as anxiety or headaches.
Therefore, sellers aren’t allowed to make health-related claims about CBD. Those that do are breaking the law.
So pure CBD won’t register on a standard drug test?
Routine drug tests don’t screen for CBD. Instead, they typically detect THC or one of its metabolites.
The person ordering the drug test could request to have CBD added to the list of substances being screened for. However, this is unlikely, especially in states where CBD is legal.
The bottom line
CBD shouldn’t show up on a routine drug test.
However, keep in mind that the industry isn’t consistently regulated, and it’s hard to know what you’re getting when you purchase a CBD product.
If you want to avoid THC, ensure that you’re purchasing CBD isolate from a reliable source.
