Cannabis has historically been thought of as a relaxant and a depressant of the physical body. As a result it’s no surprise that the idea of using cannabis to help manage blood pressure has gained some traction recently. While generally confirming the idea that cannabis can lower blood pressure, recent experiments have also shown some disagreement depending on the manner in which experiments are conducted. A review from the University of Nottingham encapsulates some of the discussion around the effect of cannabinoids on blood pressure, but for readers wanting a digested answer, the clearest part of the conversation is that cannabis use almost certainly does not contribute to high blood pressure, especially when vaporized.
High blood pressure or hypertension is a condition in which the force of a person’s blood against their artery walls is higher than normal and therefore likely to lead to a host of other problems. Although high blood pressure that occurs without symptoms often goes unnoticed, the body can only compensate for unhealthy blood pressure for a limited amount of time. Left uncontrolled, high blood pressure can lead to heart attack, stroke, heart failure, vision loss, and poor kidney functioning, all without much warning.
The general research pipeline for investigating a new area of medicine tends to flow from test tube, to rodents, and lastly to humans. Genetically modified rodents are expensive to create and time-consuming to maintain, so preliminary assays are usually first performed on the cells in question outside normal living conditions (such as in a test tube or Petri dish). In this area, cannabinoids have been established as consistent vasodilators, meaning that they cause blood vessels (such as arteries and veins) to expand, thereby decreasing blood pressure. To understand this effect, imagine the force of water spraying from a garden hose. As the size of the opening narrows, the jet of water shoots further. Just like the garden hose, often the cause of high blood pressure is the buildup of clotting molecules and fat inside of arteries, which decreases the area for blood to flow through and therefore increases blood pressure.
Unfortunately, while this vasodillation effect has been observed in numerous cell preparations, the community is still debating the cause. Anandamide, which is one of the body’s natural cannabinoids, is the most popular target molecule for research. Since anandamide is naturally produced by the body and has also been shown to influence blood pressure, the general consensus is that releasing ananamide is one of the ways in which the body regulates blood pressure. However, some research groups believe that anandamide has special receptors on blood vessel walls. Others believe that the vasodillation effects are mediated by CB1 cannabinoid receptors. Still others claim the pathway is through anandamide bonding with vanilloid receptors. This is currently the reigning view and appears most likely.
Regardless, the situation becomes more complicated when cells are inside living bodies. In animals that have been made unconscious with anesthesia, cannabinoids tend to show a triphasic (three part) response. In phase one, the heart begins to beat below its normal rate, exhibiting less force and decreasing blood pressure. In phase two, the heart begins to increase rate of blood flow and pressure increases again. In phase three, the heart rate is maintained but blood pressure falls again with relaxed arteries. Phase two can be identified as a “pressor response”, which is an increase in blood pressure based on external stimuli. Drinking water, being submerged in cold water, and taking certain medications can all trigger unique pressor responses. In this particular pressor response, the body seems to be attempting to restore normal heart functioning as a result of being exposed to cannabinoids.
A multi-phase response, despite being complex to describe, is not actually very abnormal. Many of the body’s biochemical reactions proceed sequentially or else in response to varying levels of a substance. However, what is abnormal about this situation is that researchers observe an entirely different set of behavior in animals that are not unconscious. Experiments performed on conscious rodents illustrate that the phase two pressor response is the predominant response in these animals and that blood pressure is not as significantly lowered either. This is particularly perplexing and is forcing scientists to try to isolate what causes the difference in conscious versus unconscious animals’ reactions to cannabinoids. So far, the most obvious theory involves the way that anesthesia affects the cannabinoid system. Supporting this idea, research indicates that anesthetic agents that don’t depress the CB1 cannabinoid receptor lack the large drop in blood pressure seen with anesthetic agents that do depress that receptor. Additionally, mice without CB1 receptors at all have no blood pressure reaction to anandamide. Both of these findings seem to suggest that putting mice to sleep artificially can lead to larger drops in blood pressure than would normally be observed, depending on whether anesthetic agents also affect CB1 receptors.
Looking at all of this information together, we can draw a few conclusions. For one, the way cannabis interacts with blood pressure is not as simple as flipping on or off a switch. The response instead is clearly multi-phasic, complex, and depends on a variety of situational factors. The challenge in using cannabis to reduce blood pressure will be in preventing the body from adjusting to the initial decrease, which may perhaps be achieved by using other supplements in conjunction with cannabis or else using synthetic cannabinoids that are similar to those found in cannabis. However, the most important conclusion for those reading this article is that whether cannabis itself is capable of decreasing blood pressure in humans, it is not being shown to increase blood pressure. Tobacco, by contrast, most definitely does, and as a result, many cannabis users worry whether consuming cannabis, by association, will exacerbate the high blood pressure they are attempting to manage. Judging from the latest data, those cannabis users can breathe a sigh of relief…and a dose of cannabis.
Barbara Malinowska, Marta Baranowska-Kuczko, and Eberhard Schlicker. (2011) Triphasic blood pressure responses to cannabinoids: do we understand the mechanism? British Journal of Pharmacology (2012) 165: 2073-2088.
Michael Randall, David Kendall, and Saoirse O’Sullivan. (2004) The complexities of the cardiovascular actions of cannabinoids. British Journal of Pharmacology (2004) 142:20-26.