“Opioid receptor agonist drugs, such as morphine, are very effective for treating chronic and severe pain; but, tolerance can develop with long-term use. Although there is a lot of information about the pathophysiological mechanisms of opioid tolerance, it is still not fully clarified. Suggested mechanisms for opioid tolerance include opioid receptor desensitisation, reduction of sensitivity G-proteins, activation of mitogen-activated protein kinase (MAPK), altered intracellular signaling pathway including nitric oxide, and activation of mammalian target of rapamycin (mTOR).
One way to reduce opioid tolerance and increase the analgesic potential is to use low doses. Combination of cannabinoids with opioids has been shown to manifest reduce the opioid dose. Experimental studies revealed an interaction of the endocannabinoid system and opioid antinociception.
Cannabinoid and opioid receptor systems use common pathways in the formation of analgesic effect and demonstrate their activity via G protein coupled receptors (GPCR). Cannabinoid drugs modulate opioid analgesic activity at a number of distinct levels within the cell, ranging from direct receptor associations, to post-receptor interactions through shared signal transduction pathways.
This review summarizes the data indicating that with combining cannabinoids and opioids drugs may be able to produce long-term analgesic effects, while preventing the opioid analgesic tolerance.”
“The global cancer burden is significantly increasing at an alarming rate affecting patients, relatives, communities, and health-care system. Cancer patients require adequate pain relief and palliative care throughout the life course, especially in terminal illness. Although opioid treatment is successful in majority of patients, around 40% do not achieve enough analgesia or are prone to serious side effects and toxicity. The treatment of medical conditions with cannabis and 
“For patients with chronic, non-cancer pain, traditional pain-relieving medications include opioids, which have shown benefits but are associated with increased risks of addiction and adverse effects.
“The 20% prevalence of chronic pain in the general population is a major health concern given the often profound associated impairment of daily activities, employment status, and health-related quality of life in sufferers. Resource utilization associated with chronic pain represents an enormous burden for healthcare systems. Although analgesia based on the World Health Organization’s pain ladder continues to be the mainstay of chronic pain management, aside from chronic cancer pain or end-of-life care, prolonged use of non-steroidal anti-inflammatory drugs or opioids to manage chronic pain is rarely sustainable.
“Marijuana is increasingly utilized for the treatment of multiple medical problems, including back pain, in the United States. Although there is strong preclinical evidence supporting the promise of 
“Neuropathic pain conditions including neuropathic orofacial pain (NOP) are difficult to treat. Contemporary therapeutic agents for neuropathic pain are often ineffective in relieving pain and are associated with various adverse effects. Finding new options for treating neuropathic pain is a major priority in pain-related research.
“Burning mouth syndrome (BMS) is a neuropathic pain disorder associated with a burning sensation on oral mucosal surfaces with frequently reported xerostomia, dysgeusia and tingling or paraesthetic sensations. However, patients present no clinically evident causative lesions. The poor classification of the disorder has resulted in a diagnostic challenge, particularly for the clinician/dentist evaluating these individuals. Major research developments have been made in the BMS field in recent years to address this concern, principally in terms of the pathophysiological mechanisms underlying the disorder, in addition to therapeutic advancements. For the purpose of this review, an update on the pathophysiological mechanisms will be discussed from a neuropathic, immunological, hormonal and psychological perspective. This review will also focus on the many therapeutic strategies that have been explored for BMS, including antidepressants/antipsychotics, nonsteroidal anti-inflammatories, hormone replacement therapies, phytotherapeutic compounds and non-pharmacological interventions, overall highlighting the lack of controlled clinical studies to support the effectiveness of such therapeutic avenues. Particular focus is given to the 
“Over the past decade the phenomenon of