Understanding Half-Life

The science of cannabis is an intricate and ever-evolving labyrinth of information. Many studies which would have been prohibited in the past are now gaining rapid traction. New information on cannabinoids is published on a near daily basis. 

While there is certainly much more research left to be done, the fact remains that we are conducting more studies on cannabinoids today than ever before. Part of this research involves rigorous examination of the pharmacokinetic properties of various cannabinoids.  Pharmacokinetics is the branch of pharmacology that deals with the way that drugs move through the body, rather than how they affect the body through the release of neurotransmitters.

For example, we know that the perceptible effects of cannabinoids like CBD or THC lasts only a matter of hours, but metabolites from the cannabinoids can remain in the system for days, or even weeks at a time. The duration of this is dependent on several factors, such as dose, frequency of use, method of consumption, body fat, and your metabolic rate. The impact of these influences varies from person to person, making it difficult to understand the complex relationship between our body and the movement of cannabinoids.

Thankfully, medical scientists have long since developed something called a ‘half-life,’ which provides a more consistent and reliable way of gauging the pharmacokinetic action of cannabinoids, as well as pharmaceuticals and over the counter medicines. In this article, we’ll go over everything you need to know to understand half-life and its importance in the world of cannabinoids.

What Is Half-Life?

Half-life (also called the biological half-life or elimination half-life) is the pharmacokinetic parameter used to define the period of time required for the total concentration of drugs in the body to be reduced by one half, or 50%. In short, a drug’s half-life determines the amount of time that it takes for your body to eliminate half of the starting dose. It typically takes multiple half-life cycles before a substance is completely eliminated from the body. 

The half-life of a drug is usually measured by testing the concentration of the substance in relation to plasma, which comprises of over half of your total blood content. Plasma is important because it acts as a liquid carrier for nutrients, hormones, proteins, and many other vital compounds that are distributed throughout the body. 

Cannabinoids can typically be detected in blood plasma immediately after inhalation, and hit their peak concentration in around 3-10 minutes. Studies indicate that depth of inhalation, puff duration, and the amount of time that breath is held all have an effect on the bioavailability of cannabinoids administered via inhalation, which will affect the actual dose of cannabinoids being consumed.  

Edibles have a much longer onset of effects, and thus a longer half-life, as cannabinoids that are taken orally must be absorbed by the digestive tract before they can enter the bloodstream. Cannabinoids taken sublingually enter the bloodstream immediately by penetrating the thin mucous membrane located under your tongue. 

Once in the blood, cannabinoids move on to be processed by the liver, which plays a key role in the body’s metabolic processes. Cells in the liver use enzymatic reactions to transform nutrients into a form that your body can more readily use. This process is especially important when consuming edibles, as the liver facilitates a hydroxylation reaction that converts cannabinoids into their more bioavailable counterparts, such as the conversion of THC into 11-hydroxy-THC, or CBD into 7-hydroxy-CBD, which both later turn into their inactive and highly lipid soluble carboxylated forms 11-COOH-THC and 7-COOH-CBD, as well as other metabolites. This reaction also occurs when you inhale, regardless of whether you’re smoking or vaping.

As these cannabinoids cycle through the bloodstream, they also cross through the highly selective and semi-permeable blood brain barrier (BBB), which serves as a sort of biological security guard that decides which compounds are allowed to come in and out of your brain. Blood plasma enters the BBB through the carotid and vertebral arteries, which run through the neck to the base of the skull.

It is during this process of conversion and absorption that the lipophilic or fat binding properties of cannabinoids begin to make themselves known. They move from blood plasma to adipose fat stores around the body, as well as highly vascularized tissues, such as those located in the lungs, heart, and liver. These concentrations are then re-released into the bloodstream over time, where they are eventually excreted.

Overall, the half-life of a cannabinoid serves as an easy way to understanding how quickly cannabinoids are eliminated from your body.

How Is Half-Life Related to Drug Testing?

While half-life does provide valuable insight into how long cannabinoids and other substances may stay in the system, it does not give a definitive answer when it comes to drug tests. You should not use the duration of a cannabinoid’s half-life to determine detectability for a drug test, as everyone responds differently to different cannabinoids. The half-life of a cannabinoid is only a clue.

This is why half-life is usually defined in the form of an expectable range of time, rather than a pre-defined period. Factors like body fat and metabolism play a major role in determining detectability for a drug test, and thus can have a significant impact on the half-life of lipophilic compounds, such as cannabinoids. Additionally, each cannabinoid has its own unique pharmacokinetic behavior, and is eliminated from the body at different rates. 

What Is The Half-Life of CBD and THC?

Cannabidiol (CBD) has a half-life of 18-32 hours, but can remain in the system for around 2 to 5 days. Meanwhile, delta-9-tetrahydrocannabinol (d9-THC) has a half-life that can last up to 120 hours in frequent users, and is detectable in the system for up to approximately 30 days. Other cannabinoids, especially phytocannabinoids like CBG, CBC, CBN, or D8-THC, have not yet had much definitive research on their half-lives, but they are likely to fall within a similar range as CBD and THC.

Compounding factors like dose, frequency of use, method of consumption, body fat, and your metabolic rate may affect the half-life of cannabinoids, but knowledge of the mechanisms behind these forces will better prepare you to navigate their hazards. Hopefully by the end of this article you have learned everything you need to know to understanding the importance of a cannabinoid’s half-life.

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