Table 1 Characteristics of included studies

1

Methods

Retrospective cohort study

Participants

Patients at Dartmouth-Hitchcock Medical Center enrolled in active opioid contracts for painful chronic pancreatitis

Intervention

35 out of 53 patients were registered with a state therapeutic cannabis program in either New Hampshire or Vermont. Study did not report method of use of medical cannabis (MC).

Outcomes

Opioid prescription dose was converted into a morphine equivalent dose (MED). Patients registered on the cannabis program showed a decreased mean daily opioid use of 126.6 MED (± 195.6 MED) compared to those who were not enrolled 183.5 MED (± 284.5 MED), P = 0.39. Patients enrolled in state therapeutic cannabis programs had decreased mean hospital admissions in the past calendar year as compared to the unenrolled group; P = .53 had reduced number of visits to the emergency department in the past year as compared to those enrolled in the active opioid contract (P = 0.59) and a fall in mean emergency department visits in the past calendar year as compared to patients not enrolled (P = .39). Average daily opioid use in patients at initiation time is 190.34 MED (± 273.3 MED).

2

Methods

Cross-sectional survey through online questionnaires to medical cannabis patient

Participants

244 medical cannabis patients with CP who patronized a medical cannabis dispensary in Michigan between 2013 and 2015. Survey has 46 questions detailing medical conditions for which MC was used and participants completed the 2011 Fibromyalgia Survey Criteria to stratify level of pain. Study did not report methods of use of MC.

Intervention

No intervention, however, survey was on participants who were already on medical cannabis

Outcomes

Patients with lower pain centralization had the largest reductions in opioid use as compared to those who reported higher levels of pain centralization. Mean change in self-reported opioid use was − 64%

3

Methods

Cohort study with a 4-year follow-up. Baseline interviews and self-completed surveys were used to get participants’ responses.

Participants

1514 participants, 18 years or older using opioids, recruited across community pharmacies across Australia. Although the questionnaire asked about the methods of use of MC, the study did not report on this.

Interventions

None

Outcomes

At 4-year follow-up, 24% of participants had used MC for pain. At 3-year and 4-year follow-up waves, 78% and 70% of participants with adjuvant MC usage reported no effects of MC on opioid use, respectively. Also, at 3-year and 4-year follow-up waves, 22% and 30% of participants with adjuvant MC usage reported an occasional or regular reduction of opioids when using MC.

4

Methods

Community survey of a sample of people previously prescribed opioids for non-cancer chronic pain. Study included 1514 people in Australia to collect data on cannabis use, ICD10- cannabis use disorder, and cannabis use for pain.

Participants

1514 participants who had previous prescription of medical cannabis. Study did not report on method of use of MC.

Intervention

No intervention, however, survey was on participants who were already on medical cannabis.

Outcomes

16% of the cohort used medical cannabis for pain relief on the survey month. Average pain relief was 70%. In contrast, the average reported pain relief they reported from opioid medication was 50%. Those who used medical cannabis were mostly younger, had greater pain severity, were on higher opioid doses, and were more likely to be non-adherent to the prescribed opioid medication. Of those who had used cannabis for pain relief, n = 34 felt that cannabis provided 100% pain relief; only four of these reported that their medications gave them 100% pain relief (and among all those using cannabis for pain relief, n = 10 reported 100% pain relief from their medications).

5

Methods

Cross-sectional survey of registered customers of Tilray a registered producer of medical cannabis.

Participants

301 participants (53%) used medical cannabis for chronic pain. Methods of MC use include joints (243; 90%), vaporizers (n = 234; 86%), oral/edibles (baked goods, butter, tincture, etc.) (207; 76%), and cannabis-infused topical ointments (44;16%).

Intervention

No intervention; however, survey was on participants who were already on medical cannabis

Outcomes

73% use medical cannabis for CP; 335 of participants reported substituting opioids with medical cannabis.

6

Methods

Cross-sectional survey collected via email from Canadian medical cannabis patients collected information on patterns of use and impact of medical cannabis on use of prescription drugs, tobacco, illicit substances, alcohol, and tobacco.

Participants

2032 participants, 91% Caucasian, and 62% males. Primary method of use of MC was vaporizer (31.1%), joint (30.4%) oral/edible (16.3%), pipe (11.3%) waterpipe/bong (10.4%), topical (0.3%, juicing (0.2%)

Intervention

No intervention, however, survey was on participants who were already on medical cannabis.

Outcomes

Prescription drugs were the most cited substances that cannabis was used to substitute (69.1%). 35.3% of theses prescription medicines was opiates and opioids. Patients cited the following reasons by rank for substitution: a safer alternative, fewer adverse effects, better symptom management, fewer withdrawal symptoms, ability to obtain medical cannabis, and greater social acceptance of cannabis than prescription drugs.

7

Methods

Case series of three patients who used small doses of smoked marijuana in combination with an opioid.

Participants

Patient A: a 47-year-old woman with a 10-year history of chronic progressive multiple sclerosis with significant ambulatory function from joint pain and leg spasticity. Opioid regiment was long acting morphine 75 mg per day, tizanidine 24 mg per day, and Sertraline 150 mg at bedtime.

Patient B: 35-year-old HIV positive with painful peripheral neuropathy. Opioid regiment consisted of long-acting morphine 360 mg per day with morphine sulfate 75 mg 4 times daily and gabapentin 2400 mg per day.

Patient C: a 44 year-old-man with a 6-year lower back and leg pain following a traumatic fall. Opioid regiment was long acting morphine, 150 mg per day and cyclobenzaprine 10 mg three times per day.

Methods of use of MC were smoked marijuana for the three patients.

Intervention

Patient A: 2–4 puffs of smoked marijuana at bedtime. Morphine regiment decreased.

Patient B: 3–4 puffs 3–4 times per day. The morphine regiment decreased over 2 years.

Patient C: Several puffs to one joint 4–5 time per day.

Outcome

Patient A reported improvement in pain.

Patient B reported an improvement in pain except during an infection with herpes zoster and discontinued morphine after 2 years.

Patient C reported improvement in pain and was able to reduce his dose of morphine.

8

Methods

Convenient Sampling method for s cross sectional survey

Participants

1513 participants from a convenient sampling of members of dispensaries of New England, USA, primarily from Maine, Vermont, and Rhode Island. Study did not report method of use of MC.

Intervention

215 regularly used opioids, 70% use MC for CP reported use of opioids with cannabis.

Outcomes

76.7% reported a reduction in their opioid use, slightly or a lot since initiating medical cannabis.

9

Methods

Quasi-experimental study of 37 habitual opioid users for chronic pain enrolled in the Medical Cannabis Program (MCP) compared to 29 unenrolled patients over 21 months.

Intervention

No intervention, however, survey was on participants who were already on medical cannabis. Study did not report on methods of use of MC.

Outcomes

The medical cannabis patients had 5.12 higher odds of reducing daily prescriptions of opioids with improvements in pain reduction, quality of life, social life, and activity levels.