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Pharmacokinetics and Pharmacodynamics: Cannabis In the Body

September 21


Pharmacokinetics and pharmacodynamics

Pharmacokinetics and pharmacodynamics, although unnecessarily difficult words to spell and pronounce, aren’t overly difficult concepts to grasp. Pharmacokinetics oftentimes becomes described by people as ‘what the body does to the drug’. Therefore meaning the process of extraction through to excretion. On the other hand, pharmacodynamics entails ‘what the drug does to the body’. As a result relating to the binding of receptors. That is effects felt by your bodily receptors and chemical interactions within the brain. These are both influenced by patient-related factors including genetics and age, as well as drug-related properties including marijuana’s THC/CBD content. Consequently, it’s critical that medical specialists prescribe specific doses of medicinal cannabis to different individuals.

Pharmacokinetics and pharmacodynamics


As marijuana affects everyone differently, correct dosages administered become necessary. So, as to avoid any negative side effects. For example, an elderly person is far more likely to experience an adverse reaction to cannabis than they would have likely had as a teenager. As a result, a patient must be individually assessed by a medical professional to gauge their risk factors. Therefore determining their candidacy for medical cannabis. Individual patients require different dosages. Subsequently, the standard advice being “start low, go slow,”. That is to say that the patient begins using medical cannabis at minimal dosages, slowly building their way up to the correct dose.

The average patient consumes 20-25mg of THC.  This can be either THC on its own, or combined with CBD.  Elderly people with little to no tolerance to THC for example might require lower dosages (approx. 5-10mg per day) than those who are younger or have built up a tolerance to the drug (approx. 30-35mg per day).

Entering the Bloodstream 

For example, from smoking or vaporising the original flower to swallowing an oil or capsule, cannabis become consumed in many forms. Depending on the method of consumption, the half life and intensity of effects differ very noticeably. Once inhaled, cannabis almost instantly flows through the lungs and trickles into the alveoli. There it then rapidly enters the bloodstream and takes effect on the brain’s endocannabinoid system.  However, after swallowing a capsule, per se, the product follows a slower pathway. So, it becomes absorbed into the bloodstream following the digestive system rather than the respiratory system. This process involves absorption into the digestive tract and then metabolisation in the liver before finally being transported to the brain.

Pharmacokinetics and pharmacodynamics

Within the Bloodstream 

Once entered the brain, CBD and THC bind to cannabinoid receptors (CB1 and CB2 receptors) within the endocannabinoid system.  The cannabinoid receptors play a large role in dopamine and norepinephrine levels (hormones responsible for rewards and motivation). As a result, cannabis creates sensations of relaxation, euphoria, pain modulation and other therapeutic benefits.  After smoking THC and CBD, the effects not only come up faster, but also become more intense. Also, they do not last as long as oral consumption. Depending on the individual, the effects that cannabis has on the brain last roughly around 3-4 hours.

Conversely, after oral administration the effects can last up to 12 hours, providing a far more subtle sensation. This is not dissimilar to the idea of slowly enjoying a cappuccino as opposed to taking shots of coffee. Just like food, water and coffee, cannabis and the chemical compounds it contains don’t remain in the body forever, eventually excreted.

Leaving the Bloodstream 

Marijuana takes a while to leave the bloodstream when compared to most other substances that enter our bodies. It takes approximately five days for 80-90% of the total THC to be excreted, and a similar duration for orally ingested CBD.  For comparison, Panadol only takes only six hours for the same amount to become expelled from our system.  Over 65% of cannabis is excreted as faeces and 20% as urine, leaving 15% of the THC/CBD content excreted as sweat, breath and other escape routes.

Pharmacokinetics and pharmacodynamics

Half Life and Bioavailability

A half life is a good measure of how long it takes for the body to metabolise THC. Despite cannabis having a relatively quick effect on our brain, complete elimination from our bloodstream can take days. On the other hand, it can even weeks.  An individual’s consumption patterns can affect the half life of THC in their system. it.  Regular users may take up to 13 days to metabolise half of their body’s THC whereas modest users can remove half of the substance in under two days. CBD also has a long half life of one to two days, however, this does not increase disproportionately with regular intake.

Your body does not extract all of the CBD and THC within the plant, oil or pill consumed used for therapeutic purposes. THC bioavailability averages 30%. Therefore meaning that less than half of the total THC becomes extracted from the original product, across all consumption methods. The higher the bioavailability, the less quantity of the product becomes required to obtain the same therapeutic benefits. The bioavailability differs greatly depending on the method used for consumption.

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