To date, the opioid system—the network of receptors in the body that opioid drugs attach to—is most often credited with delivering acupuncture’s reported effects as an anti-inflammatory, analgesic and anti-emetic. However, studies in recent years have found another, less-studied, but equally important receptor network may be involved: the endocannabinoid system—the same system that’s responsible for cannabis’s myriad effects on the body.
Though acupuncture can trace its roots back to China 2,500 years ago, it only really gained traction in the United States in 1971 when the New York Times columnist James Reston wrote about his appendectomy in a Chinese hospital. According to James, the doctors used acupuncture to control his post-operative pain and to his surprise, it worked.
Since the publishing of James’ article, the use of acupuncture to manage pain and a host of other maladies has soared. Like cannabis, double blind clinical research on acupuncture’s benefits is lacking. However, preliminary studies on this ancient treatment’s mechanisms are beginning to reveal how it might work and why some people are seeing positive results.
One of the key tenets of traditional Chinese medicine is the existence of a life force called qi that circulates through channels in the body, known as meridians. Acupuncture involves the insertion of needles at certain “acupoints” in the body to influence the flow of qi and bring about a positive bodily response. Typically, the practitioner manipulates inserted needles by hand to further stimulate the points of interest.
Acupuncture theory has evolved since ancient times—some practitioners no longer subscribe to the concept of qi and meridians, and new techniques such as electroacupuncture have emerged. Electroacupuncture is frequently used in clinical practice and involves the use of an electrical current to stimulate the needles.
In 1997, the National Institute of Health acknowledged acupuncture’s therapeutic effects for certain conditions like chronic pain and stroke. Since then, numerous anecdotal and scientific reports suggest that acupuncture can help ease back and neck pain; symptoms of chemotherapy, like nausea and vomiting; pain associated with osteoarthritis, especially in the knee; and the frequency of tension and migraine headaches.
Acupuncture’s growing popularity has led scientists to investigate the mechanisms underlying this practice. So far, researchers’ most accepted hypothesis is that stimulating acupoints activates certain nerves, which in turn send signals to the brain and spinal cord via various nervous pathways in the body. These signals then lead to various physical effects like pain relief and the protection of brain cells.
Because nerve signaling likely plays a key role in acupuncture’s benefits, it should come as no surprise that the endocannabinoid system—whose receptors are located throughout the body, but are most concentrated in the brain—may play a role in acupuncture’s reported effects.
RELATED: WHAT IS THE ENDOCANNABINOID SYSTEM?
For example, a landmark study conducted on rats in Chinese Medicine Journal showed that electroacupuncture could reduce brain injury in strokes caused by lack of oxygen to the brain. In 2012, the finding that endocannabinoid receptors could play a role in protecting the brain from the same type of stroke led some scientists to speculate that the endocannabinoid system could be involved in acupuncture’s previously reported benefits.
Further studies in rats have shown that electroacupuncture increases the amount of the endocannabinoids AEA and 2-AG in the brain, meaning that electroacupuncture somehow activates endocannabinoid receptors in the central nervous system.
Studies involving acupuncture and pain have found further links with the endocannabinoid system: By inducing arthritis in rats and then performing electroacupuncture at certain acupoints, scientists determined that there was an increase in CB1 and CB2 receptors—the main receptors of the endocannabinoid system.
Interestingly, by adding or subtracting compounds that affect the CB1 and CB2 receptors, researchers have determined that the receptors work independently: CB1 is primarily responsible for the perception of pain, while CB2 moderates the anti-inflammatory effects of acupuncture.
To further complicate matters, consider that the endocannabinoid and opioid systems are linked: They share space on the brain and spinal cord, and receptors from both can be found in areas of the brain that control sensations of pleasure, reward and pain. This is why cannabis and opioid drugs are able to produce similar effects like feelings of euphoria, relaxation and pain relief.
Having these two systems so close together means that they’re often able to influence each other—this phenomenon has already been noted in animal studies involving pain. It’s also the reason why cannabinoids like tetrahydrocannabinol (THC) found in cannabis can boost the pain-relieving properties of opioids like morphine.
The overlap between these two systems may also contribute to acupuncture’s pain-fighting effects. In 2003, researchers found that electroacupuncture at particular frequencies stimulated the release of endorphins, a type of opioid made by the body.
A 2011 study involving the inflamed skin tissues of rats went even further: Scientists found that electroacupuncture at a particular acupoint stimulated the release of endorphins, and through a series of tests, they also found that the endocannabinoid receptor CB2 was responsible for reducing inflammation and stimulating the release of the endorphins in these skin tissues.
Pain is one of the most common reasons people seek out acupuncture, and recent studies may give us some insight on why people continue to use it for pain management. A 2010 study involving mice found that acupuncture triggered the release of adenosine, a chemical that delivers messages between nerves cells and that also has pain-relieving properties. The researchers found a 24-fold increase in adenosine concentration in the blood of the mice after acupuncture along with an overall reduction in pain in their test subjects.
The researchers then injected the mice with compounds similar to adenosine and found a similar reduction in pain levels. They then injected more compounds that slowed the breakdown of adenosine in the body—thus boosting acupuncture’s effects by making adenosine available for a longer period of time.
This study becomes more compelling when we consider the finding that endocannabinoids regulate adenosine concentrations in the brain. Scientists have found that AEA increases adenosine levels in the brains of rats and that this mechanism is overseen by the CB1 receptor. This study, like most studies looking at the relationship between acupuncture and the endocannabinoid system, suggest that acupuncture stimulates or mimics endocannabinoid activity.
However, there are instances where the opposite has happened: Acupuncture led to a decrease in activity of the CB1 receptor. While studies like this may be outliers, they also bring up an important concept: that acupuncture may dampen effects on the endocannabinoid system to maintain balance in the body. While we’re still far away from deciphering acupuncture’s exact mechanisms, it’s clear that this treatment has tangible effects on the body—effects that are likely due to the interaction of multiple receptor systems. Understanding the complex interactions between these systems is important because they may one day lead to the development of new techniques that combine acupuncture with medicines such as cannabis that target the endocannabinoid system.
Photo credit: Antonika Chanel