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THC:CBD ratios in clinical trials

We are providing as assessment of studies where scientists evaluated the different THC:CBD ratios used in clinical studies. We are discussing the following:

What do we know about THC:CBD ratios?

The research on medical cannabis is complicated because of the abundancy of cannabis compounds within the plant. In addition, even when researchers assess only the two main components, THC and CBD, the question of what ratio to use complicates their assessment.

This is also additionally complicated because CBD may balance or counteract the effect of THC. Furthermore, patients suffering from different diseases might benefit not only from different THC:CBD ratios, but also different doses and different modes of administration.

As such, there are no current regulations or guidelines that could help the work of doctors and the situations of patients. Below, we are providing as assessment of studies where scientists evaluated the different THC:CBD ratios used in clinical studies.

Assessing THC:CBD ratios in clinical trials

Scientists performed a systematic literature review to assess all clinical trials and other research that mentioned any THC:CBD ratios. They excluded studies with approved medications, such as Sativex/Nabiximols, and animal studies. The goal was to compile ratios, the rationale for the ratio, explanation of the rationale, and minimum and maximum dosages.

The scientists found altogether 479 references, but after they excluded Sativex/Nabiximols medications and animal studies they had only 11 studies left. These studies assessed the effect of THC:CBD on MS, fibromyalgia, Autism Spectrum Disorder, refractory epilepsy, brain activity, Dravet Syndrome, complex motor disorder with predominant dystonia, spasticity, schizophrenia/schizotypal/psychosis like symptoms, and addiction/dependence.

The THC:CBD ratios tested in these studies covered a wide range:

  • 1:0
  • 22:1
  • 2:1
  • 1:1
  • 1:6
  • 1:20
  • 1:33
  • 1:50
  • 0:1

Reasons for THC:CBD ratios

Those who led the clinical trials only very rarely explained why they chose the particular ratio that they chose. When they did explain, their mostly said that this is the ratio that was available to them for the study or in their area/country. Only one study compared different THC:CBD ratios, but they simply said “high CBD:THC” and “low CBD:THC”.


The dosage also varied considerably throughout the studies, including:

  • 5 mg/day THC:10 mg/day CBD
  • 100 mg/day or 50 mg/day combined THC and CBD
  • 40 mg/day THC and 600 mg/day CB

Method of administration also varied, including:

  • Sublingual mainly for children
  • Vaporizing mainly for adults and
  • “normal” method, whatever that means…


Given the variability across countries and studies and the legality of cannabis derived products, there is a lack of research and evidence regarding what the best THC:CBD ratio might be, and what combination would be the best for what health conditions. The authors recommend some standardized way of using specific, measurable THC:CBD ratios. This would result in reliable, dose controlled substances that could be used to perform appropriate randomized-controlled trials.  Without such standardization, it is very difficult to assess THC and CBD pharmacokinetics, especially in various conditions.

Overall suggestions that have emerged for higher CBD:THC ratio are for these conditions:

  • Decreasing drug craving
  • Decreasing pain
  • Improving sleep

Furthermore, while CBD alone decreased anxiety, CBD combined with THC had no effect. However, cannabis clinical trials are very difficult to replicate due to the reasons mentioned above. As such, different studies might find contradicting results.

Scientists have acknowledged the therapeutic potential of cannabis. However, randomized clinical trials still need to provide reproducible “best practice” treatments for THC:CBD ratios, respective doses, and methods of administration.


Zeyl V, Sawyer K, Wightman RS. What Do You Know About Maryjane? A Systematic Review of the Current Data on the THC:CBD Ratio. Subst Use Misuse. 2020 Mar 3:1-5.