Cannabis is an ancient plant, with evidence of an extensive history of use. From foodstuffs and medicines to an essential craft material, this diverse crop has held significant value to numerous cultures for thousands of years. However, we will be focusing on the therapeutic potential of the plant and some of the identified applications of medical cannabis.
Cannabis is also a complex plant that contains a large number of active chemical compounds, many of which have distinct properties. While many of these compounds may have important medicinal potential on their own, they may also work synergistically to achieve an array of further medicinal benefits, often referred to as the entourage effect.
There have been a large volume of studies in recent history that have aimed to assess cannabis and its derivatives as a potential treatment for a wide range of conditions and symptoms. So, what are these reported benefits?
Medical Cannabis and Pain
A notable proportion of studies have focused on trying to answer the above question. For example, one study has found “moderate-quality evidence to support the use of cannabinoids for the treatment of chronic pain and spasticity.” 
Other studies have focused on the effects of cannabis flower on acute pain. One of these studies demonstrated a dose-dependent effect of vaporised cannabis in the management of spontaneous pain with higher ratios of THC having the strongest impact on pain scores. Further research is needed to understand this effect, although the dissociative effects of THC are expected to play at least some role. 
There is growing evidence to support the use of cannabis for other specific types of pain relief, although to date there is little evidence to suggest it will replace front line medicines like opioid-based drugs for traumatic pain.
The largest proportion of medical cannabis users cite chronic pain as the primary reason for using the products.
Medical Cannabis and Cancer Symptoms
There is a good level of evidence to support the use of medical cannabis in managing symptoms related to cancer and the side effects of chemotherapy treatments.
Several countries, including the UK, have licensed medical cannabis for chemotherapy-induced nausea and vomiting. A number of clinical studies have assessed the anti-emetic effects of cannabis, including sickness related to HIV/AIDS and chemotherapy.
Up to 75% of cancer patients experience nausea and vomiting brought on by chemotherapy treatment. One systematic review concluded that “cannabis-based medicines may be useful for treating refractory chemotherapy-induced nausea and vomiting”. Research that focuses on the anti-emetic use of medical cannabis in other settings remains relatively limited.
While research continues into the direct treatment potential of medical cannabis for various forms of cancer, there is currently not enough evidence to support its use in this area.
Medical Cannabis and Epilepsy
The established efficacy of medical cannabis in the management of treatment-resistant forms of epilepsy has had a significant influence on its reintegration as a legal therapy – particularly in the UK. The use of cannabis-based medicines for some forms of refractory epilepsy (notably Dravet syndrome and Lennox-Gastaut syndrome) was one of the early recommendations by the National Institute for Health and Care Excellence (NICE) for medical cannabis.
A number of studies have provided evidence to support this application. For example, one study showed that participants treated with a range of whole-plant medical cannabis oils experienced a remarkable reduction in seizure frequency. Furthermore, no significant adverse events were observed. Participating patients were also able to reduce the use of other potent antiepileptic drugs that tend to have severe side effects. 
Medical Cannabis and PTSD
Another frequently identified reason for using medical cannabis is for the treatment of Post-Traumatic Stress Disorder (PTSD) and other psychiatric conditions. Notably, veterans report mental health conditions including PTSD, anxiety, depression, and insomnia at higher rates than the general population and medical cannabis has been widely taken up by this community. This has led to the US VA incorporating medical cannabis into its treatment regimes for veterans.
Researchers hypothesise that cannabis’ reported efficacy in the treatment of PTSD may be due to a number of neurological mechanisms. Other factors may include improved sleep quality and reduced nightmare activity, and reductions in feelings of anxiety and depression. Growing evidence suggests that the endocannabinoid system (ECS) may play a role in processes linked to all of these factors. A recent review concluded that “there is a robust rationale for treatment with drugs that target the [ECS] and the results are promising…” 
Medical Cannabis and Anxiety
Although anxiety can be linked to PTSD it can also be a symptom of many other conditions, as well as a stand-alone mental health issue. Anxiety is the most common mental health condition with almost 20% of the US population experiencing an anxiety disorder. It is also one of the most common reported reasons for medical cannabis use globally. 
Research suggests that medical cannabis products may be useful in reducing anxiety levels; however, the two most common cannabinoids, CBD and THC, are believed to have differing effects on anxiety. For example, some studies – including a study of Generalised Anxiety Disorder (GAD) – support the potential of CBD for the reduction of anxiety levels. 
On the other hand, there are some links between sustained use of high levels of THC and increased anxiety. It is believed that the effects of cannabis in anxiety will vary depending on the individual and the products being used.
-  Whiting PF, Wolff RF, Deshpande S, et al. Cannabinoids for Medical Use: A Systematic Review and Meta-analysis. JAMA. 2015 Aug 4;314(5):520.
-  Wallace MS, Marcotte TD, Umlauf A, Gouaux B, Atkinson JH. Efficacy of Inhaled Cannabis on Painful Diabetic Neuropathy. J Pain. 2015;16(7):616-627.
-  Smith LA, Azariah F, Lavender VTC, Stoner NS, Bettiol S. Cannabinoids for nausea and vomiting in adults with cancer receiving chemotherapy. Cochrane Database of Systematic Reviews 2015, Issue 11.
-  Zafar R, Schlag A, Phillips L, et alMedical cannabis for severe treatment resistant epilepsy in children: a case-series of 10 patients BMJ Paediatrics Open 2021;5:e001234.
-  Steardo L Jr, Carbone EA, Menculini G, Moretti P, Steardo L, Tortorella A. Endocannabinoid System as Therapeutic Target of PTSD: A Systematic Review. Life (Basel). 2021;11(3):214.
-  Anxiety Disorders https://www.nami.org/About-Mental-Illness/Mental-Health-Conditions/Anxiety-Disorders Accessed April 2020.
-  Bergamaschi MM, Queiroz RH, Chagas MH, et al. Cannabidiol reduces the anxiety induced by simulated public speaking in treatment-naïve social phobia patients. Neuropsychopharmacology. 2011;36(6):1219-1226.