Every time you ingest a bioactive substance, whether Tylenol or cannabis, the compounds within get broken down in your body through several steps. These are commonly known in pharmacology by the acronym ADME–or absorption, distribution, metabolism, and excretion. This process encompasses clinical pharmacokinetics, defined as “what the body does to the drug.”
While scientists study this process in great detail when developing potential new medications, it’s also very important information for healthcare professionals to know when prescribing treatments to patients. So, let’s take a closer look at the basics before discussing how this applies to cannabis:
Absorption. There are many ways to consume substances including oral, intravenous, inhalant, topical, and other methods. Each route is associated with different rates of absorption, or the way drug compounds get into the bloodstream to take further effect.
Distribution. Once the substance has made it to into the blood, it must make its way across the body. This travel involves penetration into tissues and cells to pass through membranes and enter cells where they can act on proteins and receptors.
Metabolism. This phase can be broken up into different steps: chemical breakdown of the substance via oxidation, reduction, or hydrolysis, and synthesis of internal compounds to make the substance more water soluble. Distribution is greatly influenced by route of administration; oral consumption requires breakdown via first-pass metabolism in the gut, while inhalation bypasses this step.
Excretion. Once the body has absorbed the maximal amount of a substance, the rest is eliminated as waste in the form of fluids, solids, or air. The chemical structure of the substance will determine its route of excretion.
While these encompass the main steps, it’s important to note that each individual breaks down substances differently due to genetics, environmental factors, and the other types of substances in the body, including medications. 
Cannabinoids generally have low bioavailability, or the amount of a drug that directly reaches the bloodstream.  While, as with other substances, the higher the dose of cannabis the greater the effect, cannabinoids are lipophilic, or fat loving. This is why data have shown that eating a high-fat meal increases cannabinoid bioavailability. Luckily, scientists are working on coming up with better ways to improve bioavailability for cannabis products. 
Route of administration greatly impacts metabolism and absorption, explaining why taking a puff off a vape pen will take effect sooner than consuming an oil. Smoking may produce a bioavailability of 31%, with blood levels peaking within minutes of consumption versus an hour or two for edibles that last longer; however, these values vary greatly across studies. 
Cannabis also affects the breakdown of other medications in the body, which can cause drug-drug interactions. And this is something to keep in mind if you are taking one of the medication classes that is also broken down by cytochrome P450. 
Cannabinoid pharmacokinetics are complex and we need more data. It’s best to speak to a healthcare professional before starting cannabis, especially if you have multiple medical conditions or take several medications. While your doctor may not have all the answers, it’s always important to be honest (if you are comfortable) so you can avoid drug-drug interactions and optimize your experience.
Image Credit: Darwin Laganzon
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