The scientific explanation of half-life is a term used to measure the amount of time taken for a specific compound to be reduced to half its original effectiveness or amount within the body ( 3 ). The half-life of CBD is how long it takes for it to be metabolized and eliminated from the bloodstream.
You cannot test for the half-life of CBD by yourself at home. Scientists have researched its half-life by testing the blood plasma of study participants for traces of CBD after administering doses. By using this data, scientists worked out how long CBD stays in the body within a general timeframe.
The Half-Life of CBD
Whether you’re just starting out or a long-term CBD user, you might be wondering how long it stays in the body.
CBD Dosage Methods
CBD is short for cannabidiol, and it is a naturally occurring compound found in the cannabis plant. Cannabis has around 100 different cannabinoids, each with its own features, chemical structure, and therapeutic properties ( 1 ). CBD is arguably the most popular and well-known cannabinoid and can be isolated and purchased in CBD-based ointments, oils, tinctures, and edibles.
These reports suffered from a number of design flaws, including incomplete baseline quantification of baseline seizure frequency, indeterminate time periods for outcome determination and, in some cases, inadequate (or missing) statistical analysis—in general, a lack of sufficient detail to adequately evaluate and interpret the findings. Limitations aside, several studies did report that administration of adjunctive CBD did not result in meaningful changes in seizure frequency (11–13).
A number of difficulties exist in evaluating published data on CBD or marijuana use for epilepsy. The extremely limited published studies were small, poorly described, and not well designed. Contributing to the difficulty of interpreting published studies, CBD products are not produced under the guidance of good manufacturing practices (GMP) and are not subject to regulations governing labeling, purity, and reliability. In other words, currently, there is no guarantee of consistency between products, or even differing lots produced by the same manufacturer. Without independent testing (e.g. USP certification) of CBD products for content and purity, as well as bioavailability testing of specific products, uncertainty surrounds the use of available CBD products in routine clinical settings.
Cannabidiol pharmacological effects are mediated through G protein coupled receptors, cannabinoid type I (CB1) and cannabinoid type II (CB2), which are highly expressed in the hippocampus and other parts of the central nervous system (2). When activated, CB1 receptors inhibit synaptic transmission through action on voltage-gated calcium and potassium channels, which are known to modulate epileptiform and seizure activity (3). CB2 receptors are primarily expressed in the immune system and have limited expression in the central nervous system. The effects of CBD are CB2 receptor independent (3).
Clinical Evidence in Epilepsy
While animal experimental data clearly suggest a potential benefit, supportive clinical data are quite sparse. In a case-control study of 308 cases of new onset seizures, Brust and colleagues found that marijuana use was significantly less prevalent among men who had unprovoked seizures compared to case controls (9). This difference was not significant in women. The authors suggest a potential protective effect against seizures with marijuana use; however, this should be considered speculative.
When administered alone, CBD is an effective anticonvulsant in maximal electrical shock (MES), magnesium-free, 4-aminopyridine, and audiogenic models (7, 8). Co-administration with AEDs leads to various effects; anticonvulsant effects of CBD are enhanced with phenytoin or phenobarbital but decreased with chlordiazepoxide, clonazepam, trimethadione, and ethosuximide. In a recent study using an acute pilocarpine model, although CBD administration reduced the number of animals displaying seizure activity, CBD did not appear to have any significant effect on the number of seizures per animal (7).
Tolerability and Drug Interactions
Over the past few years, increasing public and political pressure has supported legalization of medical marijuana. One of the main thrusts in this effort has related to the treatment of refractory epilepsy—especially in children with Dravet syndrome—using cannabidiol (CBD). Despite initiatives in numerous states to at least legalize possession of CBD oil for treating epilepsy, little published evidence is available to prove or disprove the efficacy and safety of CBD in patients with epilepsy. This review highlights some of the basic science theory behind the use of CBD, summarizes published data on clinical use of CBD for epilepsy, and highlights issues related to the use of currently available CBD products.
Other targets for CBD include transient receptor potential (TRP) channels that are involved with the modulation of intracellular calcium (1, 6). Cannabinoids are highly lipophilic, allowing access to intracellular sites of action, resulting in increases in calcium in a variety of cell types including hippocampal neurons. CBD actions on calcium homeostasis may provide a basis for CBD neuroprotective properties.