Medical cannabis is most frequently administered either by smoking or vaporization or in the form of edible preparations. None of these approaches has been standardized, however, and the effectiveness of edible cannabis preparations has not been evaluated in clinical trials. Smoked cannabis has been evaluated in a small number of randomized controlled trials involving patients suffering from neuropathic pain conditions. In each of the trials, patients experienced a reduction in pain intensity at THC concentrations of 3.9 percent or higher.
A zero percent THC dose was used as the placebo condition; this formulation was created with cannabis from which all cannabinoid substances had been removed by alcohol extraction. Adverse events from these studies were mild to moderate and included drowsiness, dizziness, and dry mouth. No serious or severe adverse events were reported.
The primary purpose of medical cannabis use is symptom relief and improved function and overall quality of life. Reductions in doses (if not complete cessation) of other medications should be strongly considered. Clinical evidence of such outcomes is lacking, however, and it remains the responsibility of the treating physician and the patient to work toward the achievement of mutually agreed-upon goals.
Resourse: Britannica
