Pain is the alarm of disease, the symptom that announces that all is not right with our bodies. Whether due to an accident or illness, it is the most common reason that people seek medical assistance. But, because pain has many causes, some of which are poorly understood, it is often a complex and vexing problem to treat. There are no truly effective medicines for certain types of pain, and sometimes relief comes only at the expense of debilitating side-effects. And so, the search for new and better pain-relievers, perhaps the oldest form of medicine, continues unabated.
There are different types of pain:
- Acute pain starts suddenly and is short-term;
- Chronic pain lasts for a longer period of time;
- Breakthrough pain happens when cancer is affecting a bone;
- Soft tissue pain happened when organs, muscles or tissues are damaged and/or inflamed;
- Nerve pain happens when nerves are damaged;
- Referred pain is when pain from one part of your body is felt in another;
- Phantom pain is when there is pain in a part of the body that has been removed;
- Total pain includes the emotional, social and spiritual factors that affect a person’s pain experience;
Pain does not feel the same for everyone. Describing your pain can sometimes be a challenging exercise. Treating the cause of the pain is always preferable, but it is not always possible to understand why people feel certain types of pain.
Pain signals arise and travel to the brain by one of three main pathways, each of which produces different pain sensations:
- Somatic Pain is the feeling most people imagine when they think about pain: a message sent by receptors located throughout the body whenever an injury Somatic pain signals travel to the brain via peripheral nerves and are typically experienced as a constant, dull ache in the injured region.
- Visceral Pain occurs when tissue or organs in the abdominal cavity become stretched or otherwise disturbed, due to disease or injury. Pain signals issue from a specific class of receptors present in the gut, producing feelings of pressure deep within the abdomen. Visceral pain often seems to be coming from a different part of the body than its actual source, a phenomenon known as referred pain.
- Neuropathic Pain occurs when nerves themselves sustain injury. It is often experienced as a burning sensation that can occur in response to even a gentle touch. Neuropathic pain does not usually respond to narcotic painkillers, which relieve many other types of pain. Antidepressant or anticonvulsant drugs, as well as certain surgical procedures, may improve some cases of neuropathy.
The nerve signals that our brains interpret as pain originates in receptor-bearing cells that become activated by temperature, touch, movement, or chemical changes in their environment. Pain signals travel to the brain by one of three main pathways. Pain may be acute – short-lived and intense – or chronic, persisting for days to years. For acute pain, such as the discomfort that follows surgery, doctors typically prescribe opiates: narcotic drugs derived from, or chemically similar to opium. For chronic pain, however, opiates rarely bring relief. Even when they are effective, opiates often cause nausea and sedation that become a burden to the long-term user. At the very least, people with chronic pain develop a tolerance to opiates over months or years and so must continually increase their dosage. Clearly, better pain medications would be welcome. Might marijuana be a source of these sought-after, pain-relieving drugs?
Cannabinoids for Pain
Cannabinoids have shown significant promise in basic experiments on pain. Peripheral nerves that detect pain sensations contain abundant receptors for cannabinoids, and cannabinoids appear to block peripheral nerve pain. Even more encouraging, studies suggest that opiates and cannabinoids suppress pain through different mechanisms. If that is the case, marijuana-based medicines could perhaps be combined with opiates to boost their pain-relieving power, while limiting their side-effects.
Because of the ethical and logistical difficulties of conducting pain experiments on human volunteers, marijuana’s potential to relieve pain has yet to be conclusively confirmed in clinical studies. Only a few such studies exist, for example, Cannabinoids in the management of difficult to treat pain, Cannabis, and Pain: A Clinical Review, Medical Cannabis, and Pain Management: How Might the Role of Cannabis Be Defined in Pain Medicine?, Marijuana and muscle spasticity, to name a few.
The reason that cannabis benefits so many different illnesses and ailments boils down to the fact that some of the active pharmacological components of the cannabis plant mimic an internal chemical harm reduction system in the human body that keeps our health in balance – the Endocannabinoid System (ECS).
Cannabis and the Endocannabinoid System
The Endocannabinoid System is controlled by chemicals that our body produces, called endocannabinoids. Our endocannabinoids are responsible for keeping our most critical biological functions in balance – such as sleep, appetite, the immune system, pain and more. When the body gets out of balance and moves into a state, endocannabinoids go to work to fix the problem. The pharmaceutically active components in the cannabis plant mimic endocannabinoids and so can be effective in helping the body manage crises and restore itself after trauma when the body’s endocannabinoids are not able to restore balance alone.
The abundant cannabinoids, THC, and CBD can reduce pain at the site of injury. Both have potent anti-inflammatory properties. THC’s anti-inflammatory properties are primarily driven through the activation of CB2 receptors on immune cells, which dampens the body’s pain-inducing response to injury. CBD also reduces inflammation by blocking inflammatory mediators and shifting the activation of macrophage repair cells from the pro-inflammatory type to the anti-inflammatory type. The benefits of THC and CBD in inflammation-driven pain has been well documented.
THC can modulate pain at the level of the spinal cord and brain by directly activating CB1 receptors, and indirectly, by increasing opioid receptor activation. CBD similarly impacts pain processing by increasing levels of the endogenous cannabinoid, anandamide, which acts like THC to activate CB1 receptors.
Neuropathic pain is different from inflammatory driven pain in that it arises from damage to the body’s nervous system. And, it is quite common. Neuropathic pain affects 7-10% of people and can be the result of forceful injury, pinching or stabbing that damages nerves. Disease is also a common underlying cause of neuropathic pain. For example, in multiple sclerosis, the insulation of nerve cells that breaks down, which leads to neuropathic pain. Other diseases which cause neuropathic pain, include Parkinson’s Disease, HIV/AIDS, diabetes, and shingles, to name a few. Chemotherapy is an additional common cause of neuropathic pain due to its destructive effects on many types of cells in the body. Neuropathic pain is notoriously difficult to treat because it doesn’t result from inflammation that can be targeted by non-steroidal anti-inflammatory drugs. However, whether it’s due to disease, amputation, or chemotherapy, many are turning to cannabis for the treatment of chronic neuropathic pain. Cannabis is turning out to be a promising treatment option, and its benefits have been observed in both cancer and non-cancer-related forms of neuropathic pain across rodent models and in human clinical trials.
Central pain has recently emerged as a catch-all term for types of pain that arise from dysfunction of the nervous system. While central pain can sometimes be a result of injury, it often arises in the absence of any known cause. As a result, it can be particularly hard to treat. Fibromyalgia is a classic example of central pain, which arises from dysfunction in the way pain signals make their way to the brain and are processed. Like other types of pain, the origin of fibromyalgia is largely unknown. Because of the diversity of central pain, there are few studies investigating the benefits of cannabis in this pain category. However, the most well-established benefit of cannabis in treating central pain is for fibromyalgia. In a study of 26 fibromyalgia patients, all reported benefits from cannabis use and half stopped taking their other medications. This suggests that cannabis can provide much-needed relief for those with fibromyalgia and possibly other central pain conditions of unknown origin.
One of the most noted conclusions about the use of cannabis for pain can be found in The Journal of Pain, which is the official journal of the American Pain Society.