High-THC Flower Yields Few Serious Side Effects in Patients

Findings published in the journal Pharmacopsychiatry, based on an online survey conducted in Germany between June 2020 and August 2020 with more than 1,000 patients, debunked the claim that high-THC cannabis poses unique health risks.

“Patients were allowed to participate only if they received a cannabis-based treatment from pharmacies in the form of cannabis flowers prescribed by a physician,” the researchers explained. 

“Overall, the mean patient-reported effectiveness was 80.1% (range, 0–100%). A regression model revealed no association between the patient-reported effectiveness and the variety. Furthermore, no influence of the disease on the choice of the [medical cannabis] strain was detected. On average, 2.1 side effects were reported (most commonly dry mouth (19.5%), increased appetite (17.1%), and tiredness (13.0%)). However, 29% of participants did not report any side effects. Only 398 participants (38.7%) indicated that costs for [medical cannabis] were covered by their health insurance,” they continued. 

The researchers said that patients “self-reported very good efficacy and tolerability” of medical cannabis, and that there “was no evidence suggesting that specific [medical cannabis] strains are superior depending on the disease to be treated.”

The findings are notable given that in Europe “pharmaceutical-grade cannabis flower…contain THC levels of 20 percent or greater,” according to NORML.

NORML said that the survey’s findings “push back against claims that cannabis strains higher in THC pose unique risks to health or that there is an absence of research supporting the efficacy of medical cannabis chemovars above 10 percent THC.”

The researchers behind the survey said that they were driven to examine the matter due to the lack of research containing high-potency medical cannabis. Their findings, they said, represent “the first large study exploring the effectiveness and tolerability of different cannabis strains prescribed by physicians in Germany.”

“There is increasing evidence that cannabis-based medicine (CBM) is efficacious in many different indications, mainly chronic pain, spasticity in multiple sclerosis, and palliative care. After reintroduction in medicine, the number and type of available CBM constantly increased, ranging from pure tetrahydrocannabinol (THC) to pure cannabidiol (CBD), as well as cannabis extracts and flowers with very different THC:CBD ratios. In Germany, cannabis flowers and extracts were legalized for medical purposes in 2017. In limited exceptional cases and after approval (according to the Social Insurance Code), costs are covered by health insurance. Today (as of 2023), in Germany, more than 150 different cannabis flowers can be prescribed. However, it is largely unknown, whether particular strains and/or different concentrations of THC, CBD, other cannabinoids, and further ingredients, including terpenes and flavonoids, result in different effectiveness in different conditions,” they said.

“So far, only a limited number of studies directly compared the effects of different cannabis strains in different indications. According to data collected between 2009 and 2010 from 600 patients registered with the Vancouver Island Compassion Society and treated with medicinal cannabis (MC), the ‘more popular’ Cannabis indica strains more effectively relieved pain compared to C. sativa strains. Several characteristics were found to be similar for both species, e. g., trust in purity, route of administration, and reason for use (recreational vs. medicinal).”

Still, the researchers also noted limits to their findings, and cautioned against drawing too many sweeping conclusions.

“We failed to confirm our main hypothesis that specific cannabis strains are more efficacious in specific indications. There was also no influence of the respective indication on the choice of the MC strain,” they said. “Besides one strain, all strains preferred by participants were THC dominant with high THC concentrations. Self-reported effectiveness and tolerability of MC for the treatment of a variety of medical conditions were rated as excellent, with no relevant differences between C. sativa, indica, or hybrid. The majority of patients had used cannabis as a self-medication as well as MC prescribed by physicians for years. The overall profile of smell and taste was rated as very good. On the other hand, average cost-effectiveness was rated as poor, which is probably because the majority of patients did not get cost coverage from their health insurance.”

Other limitations include of the study include “(i) only German-speaking patients could be included, (ii) most participants came from Germany, and thus data represent only a small geographical region, (iii) only data for MC strains available in German pharmacies in 2020 could be collected; (iv) data were collected online based on self-reported diagnoses and treatment effects, (v) it cannot entirely be excluded that participants provided untruthful information.” 

But the study also “has several strengths,” they said, noting its “large sample size…relatively short recruitment time…inclusion of only patients that used MC from pharmacies prescribed by physicians…patients with a wide spectrum of different indications…relatively long time use of MC…and use of 5.9 different MC strains on average allowing comparison with respect to clinical effectiveness.”