Jump to Section
- First, a Look at opioids
- The definition and origins of chronic pain
- Insomnia, obesity, diabetes, and depression: The far-reaching consequences of chronic pain
- Traditional Treatment Options for Chronic Pain
- Alternative treatments for chronic pain
- Chiropractic manipulation
- Exercise/strength training
- Stress-reduction techniques
- Cannabis and Hemp as Alternative Treatments for Chronic Pain
- Research supporting the effectiveness of CBD and marijuana for the treatment of chronic pain
- CBD Works in Several Ways to Help Reduce Nerve Pain
- Using CBD to Treat Chronic Pain: The Bottom Line
- Can I Use CBD Oil for Chronic Pain Management?
- Which CBD Products Should I Take to Manage My Chronic Pain? How to Take CBD for Pain - Internal CBD vs. External CBD?
- Muscle Pain
- Nerve Pain
- Back Pain: Do CBD Oils or Lotions Work?
- How Long Does CBD Take to Become Effective?
- How Do I Use CBD Oil for Pain Management?
- How much CBD should I take for pain management?
- Is Vaping CBD Oil Effective for Pain Relief?
- How Often Should I Use CBD for Chronic Pain Relief?
- Full-Spectrum CBD or Broad-Spectrum CBD? Which is Better for Pain Management?
- What Are the Side Effects of CBD?
- Does CBD Cause Drug Interactions?
- Now, If You’re Wondering Why You Need to Consult With Your Doctor, There Are Several Reasons.
Over 20% of adults in the United States suffer from some form of chronic pain1(Dahlhamer et. al., 2016). The impact of this condition on individuals can be devastating, ranging from loss of income to depression and addiction to opioids.
The Journal of Pain estimates that chronic pain costs the US economy as much as $300 billion per year in health care costs and an additional $300 billion in lost productivity2(Gaskin et. al., 2012), more than heart disease, cancer, and diabetes.
If you’re reading this article, chances are either you or someone you care for suffers from chronic pain. While the economic statistics are eye-opening, what you really care about is how to manage chronic pain and whether CBD and THC may provide offer a solution.
First, a Look at opioids
Opioids have long been a mainstay in the treatment of chronic pain. However, most of the recent news about opioids has been bad. Public opinion has shifted from seeing opioids as a helpful tool to a potentially addictive health risk. Massive legal settlements with pharmaceutical companies and drug distributors such as Purdue Pharma (the maker of OxyContin), Johnson & Johnson, and McKesson have dominated the headlines.
In October 2019, the Federal Council of Economic Advisers said that during the four-year period from 2015 through 2018, the economic toll from opioid addiction was more than $2.5 trillion.3(Council of Economic Advisors, 2019) According to the National Institute on Drug Abuse, between 21% and 29% of all patients prescribed opioids for the management of chronic pain abuse them with as many as 12% becoming addicted. From 1999 to 2018, there were close to 450,000 deaths associated with opioid overdoses4(Wilson et. al., 2020) and the death rate continues to accelerate.
Against this backdrop, it’s no surprise that more and more people are interested in natural, alternative forms of treatment for chronic pain. Cannabidiol (CBD) is naturally occurring, non-addictive, and is showing potential as an alternative form of treatment for chronic pain. While cannabinoids have not yet been approved for the treatment of chronic pain by the FDA in the United States, early research indicates that they may have a positive impact when used for the treatment of pain.
The definition and origins of chronic pain
There is no universally accepted definition for what constitutes chronic pain. However, the generally accepted qualification differentiating chronic pain from acute pain is that the symptoms occur frequently and have persisted for 6-months or more.
Chronic pain can be divided into two broad categories:
There is a third category of pain called psychogenic pain which refers to pain that is exasperated by psychological factors such as stress, anxiety, depression, or fear.
It’s important to understand the cause of chronic pain in order for a doctor or other wellness practitioner to prescribe the right course of treatment. Chronic pain most commonly results from one of the following causes:
Insomnia, obesity, diabetes, and depression: The far-reaching consequences of chronic pain
In addition to the obvious symptoms, the various types of pain one may experience, there are many indirect consequences of chronic pain that can lead to further serious health problems.
Chronic pain is the #1 cause of insomnia according to a survey conducted by the National Sleep Foundation. Research conducted by Patrick Finan, Burel Goodin, and Michael T Smith, published in a report titled “The Association of Sleep and Pain” found that as many as 88% of chronic pain sufferers also suffer from loss of sleep, with 50% of them reporting bouts of insomnia. Beyond insomnia, their research concluded that both chronic pain and sleep disturbances share many physical and mental health outcomes including obesity, type 2 diabetes, and depression.5(Finan et. al., 2013)
While the links between chronic pain, sleep deprivation, and depression are not yet fully researched, one thing is clear: Managing pain is essential in order to avoid negative impacts on the patient’s quality of life.
There are many treatment options available from both traditional healthcare practitioners and alternative ones. Our aim is to heighten awareness of using cannabidiol (CBD) as a natural, alternative treatment to manage chronic pain.
Traditional Treatment Options for Chronic Pain
Since the dawn of the pharmaceutical era, healthcare providers have relied on prescription and over-the-counter medication as a primary treatment for chronic pain. The following medications are all FDA approved and most are covered under standard healthcare plans, meaning peace of mind for the prescriber and potentially lower out-of-pocket costs for the patient.
According to the American Society of Regional Anesthesia and Pain Medicine, these are among the most common medications used today to treat chronic pain.
However, as popular as these medications are among prescribers, each of these has been shown to have negative effects, especially when taken over a long period of time or in high doses. These range from physical addiction, to liver and kidney damage, and blood clots. If you suffer from chronic pain and have been prescribed any of these medications, you may want to speak with your healthcare professional about the possible long term side effects.
Alternative treatments for chronic pain
In part, because of the negative side effects increasingly associated with prescription pharmaceuticals, more and more people are turning to holistic forms of treatment for chronic pain. An advantage of alternative, holistic approaches to treating chronic pain is that if they don’t appear to work for a patient, they are unlikely to cause harm.
The adoption of alternative forms of treatment has been slowed by health insurance companies, which often don’t cover these treatments, leaving the patient to pay out of pocket. More progressive insurance companies are starting to cover these treatments, or at least offer discounts for them, as part of an overall wellness approach to managing health.
If you or someone you care for suffers from chronic pain, chances are you’ve already looked into these alternative treatments. For that reason, we won’t go into great depth here but will cite relevant research you may want to explore further.
According to a 2015 National Institutes of Health report, as many as 27 million Americans are evaluated and treated by a chiropractor each year, mostly for the relief of back pain. Despite its popularity as an alternative treatment for pain relief, evidence supporting its efficacy is fairly limited. A 2018 research study published in the Spine Journal found that chiropractic manipulation and mobilization were somewhat effective in treating the symptoms, and improving mobility, for patients suffering from chronic lower back pain.7(Coulter et. al., 2018) Chiropractic manipulation is generally considered a good but temporary solution for the relief of chronic back pain.
Many people report success in using supplements for pain relief, especially pain resulting from inflammation. Turmeric, ginger, vitamin D, omega 3s are all thought to have anti-inflammatory properties and are extremely popular in many cultures for this reason. Magnesium is also thought to have a positive impact when used to treat migraines. For more information on these supplements, as well as other less-known supplements, see Dietary Supplements for Pain: A Clinician’s Guide from the University of Wisconsin-Madison.
Cannabis and Hemp as Alternative Treatments for Chronic Pain
The use of cannabis and hemp to treat chronic pain is on the rise. Cannabinoids are the active compounds found in both cannabis and its cousin the hemp plant, with the two most notable compounds being tetrahydrocannabinol (THC) and cannabinoidiol (CBD). There are over 100 cannabinoids found in cannabis and hemp, and scientists are only starting to understand their benefits for health and wellness.
Historically, there has been limited scientific research on the effectiveness of cannabinoids mainly due to legal restrictions that have only recently been relaxed. However, research into the use of cannabinoids for the treatment of various types of pain is accelerating and the data thus far shows great promise.10(Romero-Sandoval et. al., 2017)
It is important to understand that THC and CBD may have negative interactions with the pharmaceutical medications mentioned above. CBD, for example, has been shown to exacerbate hepatocellular (liver) injury in patients who were using valproate (also known as valproic acid), a form of anti-seizure medication. If you or someone you care for is using prescription or over-the-counter pharmaceuticals to control chronic pain, make sure you check with your healthcare professional before beginning to use CBD or THC either in conjunction with–or to replace–any medications.
Research supporting the effectiveness of CBD and marijuana for the treatment of chronic pain
1. Migraines: How CBD helps
In a study published in Pharmacotherapy in 2016, researchers analyzed the medical charts of 121 patients diagnosed with Migraines, who had been treated with medical marijuana. The results showed that:
- 103 of the 121 reported that they experienced a reduction in how often they had migraines.
- On average, the number of migraines decreased from 10.4 a month to 4.6.
- 11.6% of the patients reported that marijuana helped to stop the migraine headaches.
- It was also found that “there was a substantial improvement for patients in their ability to function and feel better,” said the study’s senior author Professor Laura Borgelt, PharmD, FCCP, BCPS.
Marijuana consists of both CBD and THC. So which one is helping the migraines?
One of the theories as to why marijuana helps reduce the pain of headaches has to do with how it affects serotonin levels.
Research studies have suggested that migraine headaches may be due to low serotonin levels.
While there’s less evidence about THC, what we do know is that CBD interacts with the serotonergic system via the 5HT1A receptor, a type of serotonin receptor notably found throughout the brain–as well as other parts of the body. A 2005 study published in Neurochemical Research found that CBD tightens the bond between the 5-HT1A and the serotonin that’s already in your system.
Further, there’s evidence that CBD may suppress the degradation of Tryptophan. Tryptophan is a precursor for serotonin. Increasing the availability of Tryptophan could lead to increased levels of serotonin, which may directly impact the onset of migraines.
2. Muscle Pain: How CBD helps
According to the Cleveland Clinic, “Causes of muscle pain fall into a few general groups, as follows: injury or overuse; stress; autoimmune disease; neurological and muscle disorders; infection; obstructed blood flow, or drug side effects.”
Common to most of these causes is underlying inflammation. Inflammation is a protective measure taken by the immune system.
The fact that cannabinoid receptors are highly expressed on immune cells suggests that the Endocannabinoid System (ECS) plays an important role in the regulation of the immune system.
And, the most important role that CBD plays in helping to reduce muscle pain is to reduce inflammation. Cannabinoids, including CBD, work to reduce inflammation in several different ways.
3. Nerve Pain (Neuropathic Pain): How CBD helps
Nerves function to carry signals from the outside world for our brains to process. And, nerve pain is oftentimes a result of damage to these nerves leading to dysfunction of the signaling and at other times the cause of nerve pain is unknown.
If you suffer from chronic nerve pain, then you know that treating it is notoriously challenging. Treatment could easily progress from just one medication to a cocktail of medications and from a low dose to pretty heavy-duty doses, leading to side effects. More often than not, pain relief from conventional treatments is inadequate.
More and more, CBD is being viewed as a possible alternative to traditional pharmaceutical treatments for chronic nerve pain.
A study in Current Medical Research and Opinion published in 2007 pooled together data from 5 different studies on the impact of CBD on neuropathic pain in 41 patients.
And, they found that while on average placebo reduced pain by .8 points, CBD on average decreased pain by 1.5 points. In addition, the pain relief from CBD was retained over time, on average for at least the 6 to 10 week follow-up period.
CBD Works in Several Ways to Help Reduce Nerve Pain
A study published in the Journal of Experimental Medicine in 2012 showed that CBD injected in mice significantly suppressed chronic inflammatory and neuropathic pain by activating glycine receptors at the spinal cord. Glycine receptors play an important role in modulating inflammatory pain.
A study published in Pain in 2003 showed that animals in states of pain have a greater number of cannabinoid receptors along the nerves. Activating these receptors overall makes the nerves less likely to fire off signals to the brain.
In a study published in Pain in 2012, researchers at the University of Oxford took 12 healthy volunteers, applied capsaicin to their legs (to induce pain), gave them Cannabinoids, and then took MRI scans of their brain.
The scans showed that Cannabinoids impacted activity in the parts of the brain known as the anterior mid-cingulate cortex and the amygdala. These are both parts of the brain that plays a role in emotionally interpreting pain.
Using CBD to Treat Chronic Pain: The Bottom Line
Whatever type of chronic pain you or a loved one may be suffering from, there’s good news. Evidence continues to mount that CBD may represent a safe, non-addictive alternative to conventional pharmaceutical treatments.
However, due to the potentially negative interactions with pharmaceutical medications, make sure to consult your physician or other healthcare providers before beginning to use CBD in addition to–or as a replacement for–any type of pharmaceutical.
If you have questions about how much CBD to use, what form to use (capsules, tinctures, vape pens, etc) or how frequently to use CBD, consult a medical professional who has been specifically trained in cannabinoid medicine. You can find one nearby through standard internet search engines, or through the Society of Cannabis Clinicians: https://www.cannabisclinicians.org/
CBD for Chronic Pain Q&A with Dr. Rachna Patel
Can I Use CBD Oil for Chronic Pain Management?
Though it depends on the exact type of pain you’re experiencing, in my years of treating thousands of patients with CBD products (since 2012) one of the most common conditions I’ve treated is chronic pain, including migraines & headaches, muscle pain, and mild to moderate nerve pain. My patients have reported significant improvement in pain levels, which is consistent with the clinical research I referenced in the article. It’s important to note that severe forms of chronic nerve pain, such as Spinal Stenosis and Shingles, are not effectively relieved by just CBD alone and also need THC. Autoimmune conditions, such as Rheumatoid Arthritis, Psoriasis, Crohn’s Disease, Ulcerative Colitis, Lupus, etc. also need both THC and CBD to effectively manage the chronic pain associated with these conditions.
Which CBD Products Should I Take to Manage My Chronic Pain? How to Take CBD for Pain - Internal CBD vs. External CBD?
Migraines & Headaches
When it comes to migraines and headaches, my patients have found internal forms of CBD highly effective, whether it’s an oral, sublingual, or inhaled formulation. By contrast, they have not found external forms of CBD effective, such as CBD creams that are applied to the forehead or temples.
Overall, oral, sublingual, and inhaled formulations of CBD can reduce the frequency, duration, and severity of headaches and migraines–or prevent them completely–when taken on a regular basis. However, only the inhaled formulation of CBD is effective for treating a headache that’s already started.
When muscle pain is localized–as in a calf muscle spasm–it makes sense to use an external form of CBD, known as topicals. Common formulations for CBD topicals include ointments, salves, lotions, creams, and gels. Increasingly, CBD is being used in physical therapy and sports medicine as a component of treatments for pulled and torn muscles. In this type of application, CBD works by effectively reducing local muscle inflammation and thus, the tension associated with it.
However, CBD may also be effective for the treatment of more severe or long lasting muscle pain. When muscle pain is extensive and pervasive, as in the case of spasticity associated with Multiple Sclerosis, then an internal form of CBD, whether it’s oral, sublingual, or inhaled formulation, is a far more effective option.
As discussed earlier, nerve pain is a chronic condition that is leading more and more people to turn to CBD for effective, non-addictive relief.
Among the many patients I’ve treated for nerve pain, the vast majority have found relief by using internal forms of CBD – oral, sublingual, or inhaled. For patients suffering from overwhelming, breakthrough pain, inhaled formulations of CBD such as vape pens, provide the fastest-acting relief but aren’t long-lasting. Often, patients suffering from nerve pain find that a combination of capsules or tinctures for longer-lasting relief combined with vape pens for immediate pain relief provides the best overall results.
There are external application CBD products on the market such as gels, creams, and lotions that imply effectiveness for the treatment of nerve pain. However, in my medical practice, patients who tried these external forms of CBD only found them effective in relieving chronic nerve pain in very rare cases.
Back Pain: Do CBD Oils or Lotions Work?
Back pain may be caused by simple inflammation of local muscle groups–or by structural damage to the spine itself. How effective CBD in any form can be for chronic back pain depends on the nature of the pain.
If the pain is caused by inflammation or a simple strain of back muscles, this is typically well-managed with an external form of CBD topical, such as gels, lotions, or creams. While CBD topicals are being touted by some proponents as a wonder product for relieving back and muscle pain, it’s important to remember that human skin is quite thick and has a generally low cannabinoid absorption rate. CBD-infused topicals should be applied liberally to overcome this. CBD topicals reach peak effectiveness typically in around 90 minutes.
If your back pain is being caused by structural factors such as skeletal damage or impinged nerves, then internal forms of CBD – oral, sublingual, or inhaled – may provide relief.
How Long Does CBD Take to Become Effective?
How long it takes for CBD to take effect–and how long the benefits last in your body–varies by the method of administration:
Inhalation (CBD vaping)
Most people can start feeling the effects within 5-10 minutes of the first inhalation and the effects can last for three to five hours.
Sublingual (CBD oil or water-soluble tincture)
When you take CBD oil under the tongue, it will be processed first by the gut, liver, and other digestive organs. Sublingual consumption of CBD takes anywhere from 20 minutes up to 1 hour to take effect, with peak levels of CBD occurring in the bloodstream anywhere from 1 to six hours.
Ingestion (capsules, edibles)
Similar to CBD tinctures that are taken under the tongue, CBD capsules, gummies, chocolates, and other edibles must be processed by the gut and liver in order to have the CBD enter your bloodstream and begin interacting with pain receptors. This process takes anywhere from 30 minutes up to 2 hours to take effect.
With both sublingual and ingestible CBD it’s important to understand that once CBD enters the bloodstream and is absorbed by the body, it may remain in your system for several days. In one study, scientists found the half-life (the time it takes 50% of the amount of CBD that reached the bloodstream to be cleared from the body) to be between 2 and 5 days. People who take large amounts of CBD or who take it very frequently may develop an immunity to CBD.
For this reason, if you’re considering taking CBD for chronic pain, consult first with a medical professional trained in cannabinoid medicine, for advice on exactly how much CBD you should be taking, how frequently, and in what forms. As discussed earlier, you can find cannabinoid-trained medical professionals nearby through standard internet search engines, or through the Society of Cannabis Clinicians.
How Do I Use CBD Oil for Pain Management?
While this is a very broad topic, in general, you can use CBD oil as part of a regimen designed to reduce the severity, duration, and frequency of pain or to prevent the onset of pain altogether. CBD oil tends to take effect in 20 minutes to roughly one hour. CBD oil may work slightly faster than CBD capsules or edibles, which may take 30 minutes to an hour or longer to take effect.
CBD oil, along with CBD capsules and CBD edibles (gummies, chocolates) remain effective in the body for several days and may provide long-lasting relief. CBD inhalants (CBD vape carts) may be used to supplement CBD oil and CBD ingestibles, to provide rapid relief from breakthrough episodes of pain.
How much CBD should I take for pain management?
How much CBD you need to take varies highly from person to person and by situation. When I treat patients for chronic pain, I begin by establishing three factors: 1) severity of pain; 2) duration of pain–or how long the pain lasts once it begins; and 3) frequency of pain.
In general, the severity of pain will determine the strength of CBD I recommend. Strength is represented by how many milligrams of CBD the product contains–500mg, 1,000mg, 1,500mg, and so forth. This is found on the package labeling.
Duration of pain determines how frequently I recommend a patient take a dose of CBD. In my practice, I use the smallest doses and lowest strengths possible and add dosing frequency until the patient reaches the desired result.
Finally, the frequency of pain determines how often I recommend a patient take CBD. Because CBD is stored in the fat cells of the body and may remain effective for several days, there is a risk of building up a tolerance if taken too frequently. You can take CBD less frequently than every other day, but it is not recommended you take it more frequently.
In addition to understanding the intensity, duration, and frequency of chronic pain, in my consultations, I also find out whether the patient has taken CBD before and if so, how they took it, and how their body responded. I also learn what other medications they may be on, to assess the potential of negative interactions.
As you can see, as with any other medication or supplement, there is no single answer to the question of how much you should take. For this reason, I again encourage anyone reading this who suffers from chronic pain to seek out a medical professional trained in cannabinoid medicine rather than trying to create your own treatment plan.
If you’re going to DIY it, I suggest tracking your CBD intake in a very methodical way. Keep track of the date, the strength you’re utilizing, as well the amount you’re taking, and most importantly the effect it’s having on your pain.
To help you track your progress, I created this treatment guide for my own patients. I invite you to download and use it for free as well:
Is Vaping CBD Oil Effective for Pain Relief?
Yes, vaping CBD oil has been shown to provide rapid relief, especially from breakthrough pain where the patient just can’t wait for a sublingual or ingested product to take effect. Among my patients, I’ve seen that vaping CBD oil can be highly effective in aborting a migraine or headache or preventing further increase in the severity of a breakthrough episode of nerve pain.
Bear in mind that questions have arisen over the long term safety of vaping any substance including CBD. Please check with your medical provider and review the latest publicly-available information on studies being conducted around the safety of vaping.
How Often Should I Use CBD for Chronic Pain Relief?
There’s a common misconception that CBD products need to be taken on a daily basis. It’s only in rare instances that I have my patients take CBD products every day. In fact, I tell them to take CBD products at most every other day. You can certainly take CBD products less than every other day as well. Because CBD is fat-soluble, it gets stored in the fat cells in your body. And over time, the CBD is slowly released into your bloodstream.
The questions of how much CBD to use and how often to use it are intertwined. I invite you to download this treatment guide I created for my own patients, to help you answer these questions:
Full-Spectrum CBD or Broad-Spectrum CBD? Which is Better for Pain Management?
Full-spectrum CBD may contain traces of THC while broad-spectrum CBD contains other minor cannabinoids but by definition contains 0.00% THC.
There are some conditions of severe nerve pain, like for instance Shingles and Spinal Stenosis, where the addition of THC may provide greater relief than CBD alone. However, in my clinical experience, I’ve found THC to be of no utility in treating other types of chronic pain. For the most part, patients have reported sufficient pain relief with the use of CBD alone.
What Are the Side Effects of CBD?
An in-depth investigation of the research shows that the side effects of CBD products are usually rare, and, for most people, the benefits far outweigh the risks. Clinically, I’ve seen patients experience little to no side effects of using CBD products.
Overall, in comparison with drugs that are used for the treatment of chronic pain, CBD has a better side effect profile. In fact, because the side effects are rare, doctors are beginning to believe CBD treatment could improve patients’ compliance and improve overall outcomes.
However, despite all the benefits, there are the potential side effects of CBD that all users should be aware of.
Research shows that the most commonly reported side effects of CBD are tiredness, diarrhea, and decreased appetite & weight.
Does CBD Cause Drug Interactions?
In general, people taking prescription meds should consult with their doctor before getting on CBD Oil. And, people who take certain prescription medications especially need to consult with their doctor.
Now, If You’re Wondering Why You Need to Consult With Your Doctor, There Are Several Reasons.
In this article, we have presented evidence from research and referred to the sources, that indicates the use of CBD may be beneficial in treating pain disorders. Our intention with this article is to inform the reader but not to provide recommendations for your specific ailment. Please consult your own physician, or qualified wellness practitioner, prior to taking CBD and CBD/THC products for pain relief.
1 Dahlhamer J, Lucas J, Zelaya, C, et al. Prevalence of Chronic Pain and High-Impact Chronic Pain Among Adults — United States, 2016. MMWR Morb Mortal Wkly Rep 2018;67:1001–1006.
2Gaskin D.J., Richard P. The Economic Costs of Pain in the United States. Journal of Pain. 2012.
3The Full Cost of the Opioid Crisis: $2.5 Trillion Over Four Years Council of Economic Advisors. 2019.
4Wilson N, Kariisa M, Seth P, et al. Drug and Opioid-Involved Overdose Deaths—United States, 2017-2018. MMWR Morb Mortal Wkly Rep 2020;69:290-297.
5Finan PH, Goodin BR, Smith MT. The association of sleep and pain: an update and a path forward. Journal of Pain. 2013;14(12):1539-1552.
6Vickers AJ, Vertosick EA, Lewith G, et al. Acupuncture for Chronic Pain: Update of an Individual Patient Data Meta-Analysis. Journal of Pain. 2018;19(5):455-474. DOI:10.1016/j.jpain.2017.11.005.
7Coulter ID, Crawford C, Hurwitz EL, et al. Manipulation and mobilization for treating chronic low back pain: a systematic review and meta-analysis The Spine Journal. 2018.
8Chang WD, Lin HY, Lai PT. Core strength training for patients with chronic low back pain. Journal of Physical Therapy Science. 2015.
9Cherkin DC, Sherman KJ, Balderson BH, et al. Effect of Mindfulness-Based Stress Reduction vs Cognitive Behavioral Therapy or Usual Care on Back Pain and Functional Limitations in Adults With Chronic Low Back Pain: A Randomized Clinical Trial.
Journal of the American Medical Association. 2016.
10Romero-Sandoval, E.A., Kolano, A.L. & Alvarado-Vázquez, P.A.
Cannabis and Cannabinoids for Chronic Pain. Curr Rheumatol Rep 19, 67 (2017).