Can THC Stop Neuropathic Pain?

The activation of CB1 Receptors reduces the sensation of pain in the animal body.

Chronic pain is the most common reason for taking medical cannabis. Neuropathic pain is a form of chronic pain relating to injury or disease of the nerves.  There are a number of studies, including large, human clinical trials, on the effectiveness of cannabis for treating and managing chronic neuropathic pain. So, what is the science behind cannabis as a treatment for neuropathic pain? How does it work?

Neuropathic Pain Engaged in CB Receptor Signaling

The human body has an endocannabinoid system that consists of several receptors and molecules that circulate through the body and activate or inhibit the action of these receptors. There are two cannabinoid receptors, CB₁ and CB₂, which are classified as G-protein coupled receptors that send signals to the cell to regulate a large variety of cellular processes. The endocannabinoid system plays a role in the body’s detection and transmission of pain, although the exact mechanism is complex and not fully known.

The central nervous system hosts the most CB₁ receptors. However, they do exist in other kinds of cells throughout the body. This receptor is the one primarily activated by delta-9-tetrahydrocannabinol (THC) and triggers the high that follows taking THC. Pain transduction also appears to involve the CB₁ receptor. Specifically in how it helps the body control the experience of pain. For example, mice with no CB₁ receptors in their peripheral nervous system seem to feel pain more strongly.

Also involved in this process are CB₂ receptors. This is because mice with no CB₂ receptors appear to feel pain more strongly. These receptors are primarily located in the cells of the immune system. But, they are found in other kinds of cells as well, much like CB₁ receptors. CB­₂ receptors have been found in tissues that are responsible for transmitting pain signals, such as dorsal root ganglion sensory neurons and in the spinal cord.

THC May Suppress Pain Sensation in Nerves

The effects of cannabinoids like THC, cannabidiol (CBD), and others have been studied in various animal models of pain to discover their efficacy and mechanism of action. An animal model of nerve injury is one way researchers can simulate neuropathic pain in animals. Studies on different nerve injury models have found cannabinoids appear to suppress the nerve stimulation that leads to pain sensations. Activation of CB receptors appears to prevent pain development after injury. In addition, using CBD reduced sensitivity to pain, but this is perhaps through a different kind of receptor, called the transient receptor potential cation channel, or vanilloid receptor (TRPV1).

Scientists are developing diabetic pain models in mice to represent a different kind of neuropathic pain. THC dampened the pain signals in mice experiencing diabetic neuropathic pain. Also, researchers found that THC works better than morphine alone. However a low dose of THC together with morphine enhanced the pain relief of morphine. This means taking both THC and morphine together could reduce unwanted side effects, and lower the doses of each.

Human Trials With THC and Pain

There have been a number of human clinical studies on the use of cannabis for treating pain. In general, these studies have found a dose dependent effect of THC on pain reduction. Both human and animal studies have had great similarity. Cannabinoids taken in combination with opioids (like morphine) also appear to be more effective. Consequently, these patients require lower doses of opioids. These studies also found that cannabis improves the quality of sleep in patients with neuropathic pain. On top of that, taking combined THC and CBD (in a drug called Sativex) reduced muscle spasms. Combining THC with CBD can help to minimize the psychotropic effects of THC, something not always desired in pain patients.

Neuropathic pain can be reduced by the use of cannabis. The mechanism of pain relief is complex, but involves the endocannabinoid receptors present in the peripheral nervous system. Activating the endocannabinoid receptors CB₁ and CB₂ reduces the sensation of pain. Therefore, patients suffering from neuropathic pain can enjoy a higher quality of life.

Cannabinoids for Neuropathic Pain?

Not all studies report changes in patients’ neuropathic pain as completely changed. In fact, some patients still have pain even after beginning treatment with cannabis medicine. However, many studies show that cannabis can help lower patients’ intensity of pain and sleep hygiene. This should underscore the need for further long-term safety and efficacy studies. Further, it should push patients with neuropathic pain to speak to their doctor about the potential of using cannabis medicine.