lawrence ringo tending to mature buds in a cannabis production field while smoking a joint


Changing CBD To THC Ratios In Marijuana

This study summary provides fact-based answers about the changing concentrations of THC to CBD in marijuana.

  • learn exactly how cannabinoid ratios have changed in black-market cannabis
  • know the adverse effects of rising THC levels and decreasing CBD concentrations
  • find out how the chemistry of black market cannabis has changed over 17 years

If you don’t find an answer in this guide to a question you have, leave us a comment below. We’ll search the published studies to see if an answer exists and get back to you.

Let’s get started.

2019 Study: Over 17 years marijauan THC content went up 304%. CBD levels were unchanged. #cbd #cannabis tell a friend


Study Results

From 2000-2017 the THC:CBD ratio in recreational marijuana seized from the black market increased 314%.  The THC to CBD ratio rose from 1.4/1 THC:CBD to a peak of 4.4/1 THC:CBD. (1)


cannabinoid content effects

thc cbd ratio



CBD regulates how THC makes you feel.

  • CBD is known to “down-regulate” THC absorption and decreases feelings of anxiety.  (2)

cannabidiol thc ratio


  • THC is known to cause anxiety and mental health problems in some individuals.   (3)


thc mental health


THC increase


THC content grew dramatically from an average of 8.3% in 2000 to an average of 25.3% by 2017 while CBD content remained constant at about 6%. (4)


cannabidiol bowel study


New CBD Study Published August 21 2019



 Illicit marijuana seized from the black market in Denmark from 2000-2017 was tested for THC and CBD content.

CBD THC ratio


  • The aim of this study was to see how the overall content of THC and CBD changed over time.
  • The research also studied how the ratio of THC to CBD changed in recreational marijuana. (5)



THC causes anxiety in some people while CBD is believed to relieve anxiety.

  • CBD also regulates (or “down modulates”) how THC interacts with the CB1 receptor in your endocannabinoid system.
  • An increasing ratio of THC vs CBD may account for a rise in anxiety symptoms among recreational marijuana smokers while intoxicated. (6)

medical cannabis cbd

  • THC rose from a mean average in 2000 of 8.3% to a mean average THC content in 2017 of 25.3%.
  • CBD average content remained stable during this time period.
  • After 2011, low THC recreational marijuana was no longer available in the black market. (7)


thc cbd ratio



This dramatic rise in THC—and the ratio of THC to CBD—may pose a risk to public health. (8)


We Disagree


As to THC posing a public health risk, we respectfully disagree but marijuana smokers should be aware of the changing nature of their “high” and some of the biological reasons for the change.

One of the benefits of legalization is better knowledge and sharing of scientific information about marijuana and hemp.



Download The CBD Research



Video: Dr. Ruth Ross on cannabinoids and the endocannabinoid system.




Rømer Thomsen K, Lindholst C, Thylstrup B, et al. Changes in the composition of cannabis from 2000-2017 in Denmark: Analysis of confiscated samples of cannabis resin. Exp Clin Psychopharmacol. 2019;27(4):402–411. doi:10.1037/pha0000303


Study Authors



Rømer Thomsen K

Centre for Alcohol and Drug Research


Lindholst C

Department of Forensic Medicine


Thylstrup B

Centre for Alcohol and Drug Research


Kvamme S

Centre for Alcohol and Drug Research


Reitzel LA

Department of Forensic Medicine


Worm-Leonhard M

Department of Forensic Medicine


Englund A

Department of Psychosis Studies.


Freeman TP

Addiction and Mental Health Group (AIM)


Hesse M

Centre for Alcohol and Drug Research


Keywords: Cannabis sativa; cannabidiol; endocannabinoid system; THC;

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