Cellular Biology: How Cannabis Works in the Body

Cellular Biology: How Cannabis Works in the Body

Cannabinoids are delivered to the bloodstream through the lungs (when inhaled), the digestive system (when consumed) or the skin (when applied topically). Once in the bloodstream, they are available to the brain and central nervous system.

Inhalation is the fastest method, with peak blood levels achieved within 20 minutes. Oral ingestion is slower because the cannabinoids go through the gastrointestinal tract before entering the bloodstream – which takes more time. The bioavailability of cannabinoids in the body is an important area of ongoing research with implications for the medicinal use of Cannabis. Please see an example of cannabinoid bioavailability below.

Cannabinoid Bioavailability: Example, THC

Typical plasma levels of THC after smoking Cannabis are 70-160 nanograms per milliliter (ng/ml). Because THC is lipid-soluble, it rapidly leaves the bloodstream and goes into the fatty tissues of the body. When Cannabis is smoked or inhaled, only about 10-25% of THC is absorbed into the bloodstream from the lungs and about 1% of that reaches the brain rapidly. This is important because brain cells possess unique binding sites for cannabinoids called cannabinoid receptors. When cannabinoids bind to these receptors, they trigger the pharmacological effects such as pain mitigation, nausea suppression and appetite stimulation. After the patient stops ingesting Cannabis, plasma levels of THC typically decrease to less than 20 ng/ml within 30-45 minutes. Pharmacological activity peaks at about 20 minutes after inhalation and is gone within 3 hours. When ingested orally, the pharmacological effects of THC are delayed by 30-90 minutes, peak after 2-3 hours and last for 4-12 hours. Bioavailability by ingestion is affected by liver metabolism and varies greatly (4-12%), making oral treatments difficult to manage.

In 1988, a major breakthrough in our understanding of Cannabis took place when American scientist Dr. Allyn Howlett discovered cannabinoid receptors in the human brain. Basically, these receptors are protein molecules embedded in cellular surfaces that receive chemical signals from other cells. These signals result in a range of effects from pain to nausea and euphoria to depression. They can stimulate or suppress appetite or growth, while also impacting mood and perception. Cannabinoid receptors have also been discovered in mammals, birds, fish and reptiles.

There are two major types of cannabinoid receptors in our bodies, CB1 and CB2. The CB1 receptors are found in the central nervous system, on brain cells and in the peripheral nervous system The CB2 receptors are generally found on immune cells Humans have many thousands of receptors that we still have not identified or fully understood. A common characteristic is that receptors bind with naturally-occurring substances such as hormones (e.g., estrogen, testosterone) and growth factors (e.g., insulin) as well as with exogenous substances introduced into the body to mimic the effect of endogenous substances.

Substances that activate receptors after binding with them are called agonists Those that suppress the ability of the receptor to activate are called antagonists Generally, agonists have the effect of turning receptors on while antagonists turn them off. As a result, the signal running along the neural pathway where the receptor is located is either enhanced or suppressed. Cannabinoids have been shown to stimulate the CB1 and CB2 receptors in a number of ways, serving as agonists, antagonists or as both.

Having discovered cannabinoid receptors, scientists began to search for the naturally-occurring ligand that binds with the receptors to achieve a biologic purpose. Their research uncovered two endocannabinoids and 2–AG. Both are agonists that influence pain, appetite, motor learning and synaptic plasticity.

In the bloodstream, exogenous cannabinoids act like endocannabinoids, binding with receptors to mitigate pain, suppress nausea, decrease ocular pressure and enhance appetite. Thus, as far as we know, Cannabis does not cure anything. Instead, the plant’s active ingredients can deliver important palliative effects. Note: the stimulation of the CB receptors by exogenous cannabinoids is complex, as not all cannabinoids interact with the receptors in the same way. Because of this, scientists are still trying to unravel the details of the system and its implications for medicine.

Currently, medical Cannabis is used to treat the symptoms – and the side-effects of treatments for – cancer, Crohn’s Disease, epilepsy and other seizure disorders, glaucoma, multiple sclerosis, neuropathic pain, rheumatoid arthritis and cachexia. Medical studies are exploring the use of Cannabis to suppress muscle spasms and spasticity, relieve chronic pain, manage glaucoma and bronchial asthma.


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