Cannabinoids (THC, CBD)

Testing & Sampling Times:

The cannabinoids are characterized by half-lives that are less than 12 hrs, indicating the potential need for q 12 dosing intervals, depending on the therapeutic indications. This also suggests both a peak and trough are important. In the absence of evidence, and not knowing if peak or trough concentrations are more relevant to predicting response, the wisest approach would be to measure a peak and trough, determine the patient’s half-life and from that point on, potentially trough concentrations. If the patient cannot stay for a 2 and 12 hr sample (or 2 and 24 hr sample), the trough can be collected just before the next dose, the patient can be dosed, and the peak collected at 2 hrs. Note that if the half-life is short in the patient and the interval is 24 hrs, concentrations may not be detectable at 24 hrs.

Therapeutic Range:

A therapeutic reference interval has not been established. One paper in humans suggests 10 to 100 ng/ml as a target for epilepsy, but other papers indicate concentrations above 100 ng/ml are indicated (all based on CBD). CBD is sufficiently safe that concentrations between 100 and 500 ng/ml are likely to be well tolerated.


“Steady-state” should occur in 3 to 5 drug half-lives, or 2 to 3 days after dosing at the same dosing regimen. We generally recommend monitoring at 1 to 2 weeks for drugs with a short half-life.

In the absence of a scientifically established therapeutic range, monitoring should take place for one of several reasons:

Once your patient’s therapeutic range has been established, then monitoring should take place as with any anticonvulsant/antianxiety etc.

Other considerations:

If your patient is receiving another drug that can be monitored and especially if it is metabolized by the liver, consider monitoring that drug prior to starting CBD and again 2 to 8 weeks after starting CBD to detect any potential drug interactions.