Cannabidiol (CBD) is available in many consumer products and is also the subject of extensive medical and scientific research, but how long does it remain in the bloodstream after use?
The answer depends on factors such as the dose, formulation, frequency of use, and the sensitivity of the test being used. Although standard drug tests are designed to detect THC rather than CBD, researchers measure CBD concentrations in blood samples to understand how long it remains detectable after use.
In this article, we’ll examine the factors that influence CBD’s detection window and review findings from a recent study investigating how long different oral doses of CBD remain detectable in plasma.
At a Glance
- CBD may stay detectable in the blood for roughly 3–25 days, depending on the dose taken and individual factors such as metabolism and how often it is used.
- Higher doses last longer. One analysis estimated that each extra 100 mg of CBD could extend the detection window by about four days.
- On that basis, 100 mg, 300 mg and 600 mg doses may remain detectable for around 5, 13 and 25 days respectively. These are estimates and vary between people.
- CBD can linger in the blood after its effects have worn off, but it is not routinely screened for in most standard drug tests.
Can CBD Be Detected in a Blood Test?
Yes, cannabidiol (CBD) can be detected in blood tests. However, it’s not a compound that is routinely tested for outside of clinical research studies. Most cannabis drug tests are designed to detect tetrahydrocannabinol (THC) and its metabolites rather than CBD.
How Do Clinical Researchers Measure CBD in the Bloodstream?
Clinical researchers measure CBD in the bloodstream by taking blood samples from participants at set time points after dosing and analysing the plasma for CBD and its metabolites. This allows researchers to track how concentrations change over time and calculate the ‘window of detection’, the length of time CBD can still be reliably detected in a blood sample.
As patient and clinician interest in the potential of cannabis-derived compounds such as CBD continues to rise, it is essential that clinical procedures regarding their research are thorough and supported by the most recent evidence. For example, clinical trials comparing pharmacological interventions (in this case, CBD) to placebo and/or active controls tend to be conducted using either a ‘parallel-group’ or a ‘crossover trial’.
While a parallel-group study involves each participant receiving only one treatment (e.g., CBD or placebo), those in a crossover design will receive all available treatments, separated by an adequate washout period. Therefore, the authors of a recent review note that “studies eliminating the ‘window of detection’, or length of time treatments can persist in biological matrices, are useful.”
How Is the Washout Period of CBD Measured?
A washout period is the amount of time needed to ensure the last treatment has been cleared from the body before the next treatment is administered.
Currently, the most common method for calculating adequate washout periods involves multiplying the half-life (the time it takes concentrations to halve in the blood) by a factor of between 5 and 10. According to this rule, CBD, which has been reported to have a half-life in plasma of 14.43 hours, can be predicted to wash out within 3 to 6 days.
However, the authors of the current study note that this practice is somewhat arbitrary and so it may underestimate washout periods, which in turn may affect the results of often costly clinical trials.
How Does the Window of Detection for CBD Differ from THC?
A ‘window of detection’ is the timeframe in which a specific substance can still be reliably detected in the testing of a biological sample.
It is suggested that the window of detection for CBD may be in line with that of THC, which has been found to be greater than 5 days in daily cannabis users. Both CBD and THC are lipophilic compounds, meaning they are readily stored in and slowly released by fatty tissues – though more so, THC.
However, as CBD is often administered at higher doses in clinical settings, the researchers suggest that it seems likely to have a similarly long window of detection. This theory appears to be supported by the findings of past studies.
Recent study and research
To better understand how long CBD remains detectable in the bloodstream after a single dose, researchers analysed data from three clinical trials involving both healthy volunteers and individuals with chronic health conditions. Below is an overview of the trial designs, methods and key findings.
Design and Methods of the Study: How Long Does a Single Oral Dose of Cannabidiol Persist in Plasma?
A Summary:
- Researchers analysed data from three previous clinical trials which assessed both healthy participants and those with chronic conditions who had taken a single oral dose of CBD.
- Each study measured whether CBD, THC or any other cannabinoids were present in their blood plasma 7 or more days after the initial dose.
- The goal of each study was to understand the ‘window of detection’ of CBD and the factors that influence its duration.
The researchers performed a secondary analysis of data collected in three clinical trials (CTs). The three studies recruited: (CT 1) healthy males aged between 18 and 45 years; (CT 2) individuals aged between 35 and 60 with chronic insomnia disorder; and (CT 3) healthy individuals aged between 18 and 65. All participants were instructed to avoid using cannabinoids throughout the study period.
Participants in CT 1 were administered one 300 mg dose of CBD at 9:00 am; participants in CT 2 were administered one 200 mg dose of CBD and 10 mg of THC at 10:00 pm; and participants in CT 3 were administered one dose of 15 mg, 300 mg, or 1,500 mg CBD per treatment session (each dose was made up to an equivalent volume with the addition of placebo) at 9:00 am.
Plasma cannabinoid concentrations were measured at baseline and approximately 75-, 155-, 205- and 265-minutes post-treatment in CT 1; at around 11 hours post-treatment in CT 2; and at baseline and roughly 45-, 75-, 180- and 240-minutes post-treatment in CT 3. However, the current investigation only assessed measures obtained at baseline in CTs 1, 3 at 11 hours post-treatment in CT 2.
Participants were included for analysis if their plasma cannabinoid concentrations were measured at ≥7 days after CBD use. The proportion of participants with detectable concentrations of CBD, 7-COOH-CBD, 7-OH-CBD, 6-OH-CBD, THC, 11-COOH-THC and 11-OH-THC in plasma ≥7 days after consuming a single oral dose of 15, 200, 300 and 1500 mg CBD was calculated. Zero-inflated negative binomial mixed-effects regression analysis was then used to determine whether certain demographic factors influenced residual plasma cannabinoid concentrations and to estimate the ‘window of detection’ (the length of time cannabinoids persist in plasma).
Results of the Study
A Summary:
- 24 out of 54 blood samples from a total of 32 participants contained traces of CBD more than seven days after their treatment.
- The higher the dose of CBD, the longer it remained in the body, with higher doses potentially remaining in the bloodstream for up to 25 days. Smaller doses of around 15 mg disappeared relatively quickly in comparison.
- A byproduct of the breakdown of CBD, 7-COOH-CBD, was observed more frequently than CBD at concentrations of around 20 times higher. This is likely because 7-COOH-CBD does not absorb into the body’s fatty tissue in the same way as CBD.
A total of 32 participants (CT 1 = 5; CT 2 = 10; CT 3 = 17) were included in the final review. All 17 participants in CT 3 provided more than one eligible blood sample as they received several different treatments throughout the investigation. Therefore, the total number of participants providing blood samples ≥7 days after 15, 200, 300 and 1500 mg CBD was 12, 10, 19 and 12, respectively. Eight of the latter 12 also provided a second blood sample ≥14 days after 1500 mg CBD (Time 2).
Overall, a large proportion of participants (24 out of 54 blood samples) had detectable concentrations of CBD in plasma ≥7 days post-treatment. Furthermore, the likelihood of detecting CBD, and the specific concentration observed, increased with dose, and decreased over time. The results of this analysis suggest that every 100 mg increase in the dose of CBD extended the window of detection by approximately 4 days. This would mean that doses of 100, 300, and 600 mg of CBD could be predicted to persist in plasma for an average of 5, 13 and 25 days, respectively, while doses in the ‘nutraceutical’ range (e.g., 15 mg) likely have limited persistence.
7-COOH-CBD (a metabolite of CBD) was also observed more frequently than CBD and present at concentrations around 20 times higher. This is consistent with previous pharmacokinetic studies of oral CBD which have revealed that 7-COOH-CBD reaches higher concentrations in plasma than CBD. As 7-COOH-CBD is not as lipophilic as CBD, this prolonged persistence may not reflect accumulation in adipose (fatty) tissue.
The researchers note that while current findings suggest “that low residual plasma CBD concentrations, particularly, those <1.75 ng/ml, are unlikely to elicit substantial carryover phenotypic or disease-modifying effects in crossover studies”. This remains an undesirable potential confounder that is best avoided. It is recommended that crossover studies involving CBD should, therefore, be conducted with caution, particularly when higher doses and/or chronic dosing regimens are used.
Conclusion
The findings of this study provide further context for medical professionals and patients alike regarding how long CBD may remain detectable in the bloodstream and how the dose of CBD impacts its ‘window of detection’.
To find out more about testing for cannabinoids, explore our guide on how long cannabis stays in your system.
