Cannabinoids and Chronic Pain
According to the IASP (International Association for the Study of Pain), pain is defined as an “unpleasant sensory or emotional experience associated with actual or potential damage to a tissue, or described in terms of such damage.” Worldwide, pain is one of the most frequent causes of medical consultation and has a huge influence on the quality of life and overall functioning of the patient. It is a subjective symptom as each patient feels it at a different intensity, as everyone has their own pain threshold. This threshold depends on the sensory part that indicates that something in the body has been altered, and the biological-somatic part where the psychic dimension and personal interpretation has influence. It is classified, according to its duration in time, as acute and chronic.
“Chronic pain is characterised by a duration of more than
3 – 6 months”
Chronic pain is characterized by a duration of more than 3-6 months, it may persist even if the cause has disappeared and can be sub classified into nociceptive pain (caused by inflamed or damaged tissue that activates the nociceptors of a intact nervous system) and neuropathic pain (caused by an injury or dysfunction in the nervous system).
Due to the high prevalence of pain and the difficult analgesic control of certain types of pain (e.g. chronic and neuropathic pain), one of the fundamental objectives of pharmacological research is the search for new analgesic drugs that present advantages over the existing ones. The discovery of the endocannabinoid system, and its revelation as a central and peripheral neuro-modulation system, have attracted attention to its therapeutic potential as modulators of ,especially in diseases such as cancer, multiple sclerosis and fibromyalgia, among others.
Effects of cannabinoids
- Cannabinoids reactivity decreases pain
- Helps opioid replacement
- Treatment for neuropathic pain
- Treatment for postoperative pain
The analgesic effect of cannabinoids is one of their best-characterized effects. The results of the studies suggest that cannabinoids could offer some benefit as adjuvant treatment of chronic pain.
Types of cannabinoids that interact with chronic pain
Since the nineteenth century scientist have been investigating the analgesic power of cannabinoids in numerous experiments with animals, and given that humans have cannabinoid receptors in various structures involved in the modulation and transmission of pain, it seems to be a logical consequence to prove its use as an analgesic in situations where current drugs are not effective or produce serious side effects.
To understand the analgesic potential of therapeutic cannabis, it is crucial to understand the relationship between the mechanisms of transmission of painful stimulus and the endocannabinoid system.
“The activation of cannabinoid receptors, present both in the medulla and the brain, inhibits the transmission of these pain signals”
The analgesic properties of cannabinoids are basically due to the presence of cannabinoid receptors CB1 (and in a lesser amount CB2, and TRPV) at the level of the central and peripheral nervous system. A pain stimulus comes through the nerve pathways to the spinal cord and from there it is transmitted to areas of the brain related to pain processing. The activation of cannabinoid receptors presents both in the medulla and the brain inhibits the transmission of these painful signals. At the peripheral level, in addition to inhibiting the transmission of signals, the activation of CB2 receptors reduces the release of pro-inflammatory mediators at the site of the lesion.
The endocannabinoid system is frequently located along with the most powerful and well-known pain control system: the opioid system. Both are present in the main nervous structures involved in the transmission of pain and researchers have seen a synergistic effect between both systems in the control of pain (Mazanas et al.,1999; Yesilyurt et al., 2003)
In a double-blind cross-study conducted by Wilsey B., thirty eight patients with central and peripheral neuropathic pain were observed to undergo cannabis treatment. Here it was verified that there was an analgesic response to these patients, and the psychoactive effects were minimal and well tolerated. 
However, in the study ‘Clinical Pharmacology and Therapist‘, no significant change was observed in the concentration/time in morphine plasma (opioid) after exposure to cannabis, but a significant reduction of chronic pain was observed after the addition of vaporized cannabis. Therefore, it was concluded that: “vaporized cannabis increased the analgesic effects of the opioids without significantly altering the levels of it in the plasma, allowing this combination to reduce the doses of the opioids, along with reducing its secondary effects” 
Based on these data, it can be concluded that the joint administration of cannabinoids with opioids could enhance the analgesic effect of the opioids, and offer safer advantages. Cannabinoids can reduce the number of opioids that are needed and consequently they can reduce the appearance of side effects from these.
Bibliography for Cannabinoids and Chronic Pain
 Wilsey B, Marcotte T, Tsodikov A, Millman J, Bentley H, Gouaux B, Fishman S. “A randomized, placebo-controlled, crossover trial of cannabis cigarettes in neuropathic pain“. J Pain. 2008 Jun;9(6):506-21. doi: 10.1016/j.jpain.2007.12.010. Epub 2008 Apr 10.
 D. I. Abrams, MD, C. A. Jay, MD, S. B. Shade, MPH, H. Vizoso, RN, H. Reda, BA, S. Press, BS, M. E. Kelly, MPH, M. C. Rowbotham, MD and K. L. Petersen, MD. Cannabis in painful HIV-associated sensory neuropathy A randomized placebo-controlled trial. Neurology February 13, 2007 vol. 68 no. 7 515-521
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