The the data shown above was posted by an Oklahoma City cannabis testing lab on the r/OKMarijuana subreddit. I am not affiliated with them, but I thought that their data might be interesting to customers who are curious of THC levels that you would typically find in cannabis flower and distillate. The sample size is large enough to be representative of the value distribution of THC in different strains of marijuana flower typically sold in Oklahoma. It is also probably representative to most medical marijuana sold in other states.
The most typical amount of total THC you will come across is between 15-20% based on mass. This is a roughly Gaussian distribution, and very seldom will you ever come across a marijuana strain that is over 30%. Approximately 3 out 1695 samples exhibited total a total THC content above 30%. You will also seldom come across a strain that is less than 5%, although the number in this group is higher.
When determining total THC concentration it is important to note that the following equation is used to calculate total THC.
THC + THCa*0.877 = total THC
This equation takes into account that the product will be burned, which decarboxylates THCa into bioactive THC. This equation also takes into account the molecular mass difference between THCa and THC with CO2 coming off in the combustion. It is important to take this ratio into consideration because most of the available THC in cannabis flower is in the form of THCa, which is not psychoactive.
The following graph denotes typical total THC concentrations in distillates as provided by an Oklahoma City cannabis testing lab on Reddit.
From the data, it appears that most THC concentrates typically vary between 60-90%. The distribution is not Gaussian, and most likely is the result of how well the THC is separated (if that is the intention), what extraction method is used, and what is intended to be in the extracted concentrate. It is not just THC that affect the endocannabinoid system. All of the different terpenes and all of the different cannabinoids that are present in the cannabis plant in its natural form that affect the endocannabinoid system. As a result, some places might choose a full spectrum extract where natural terpenes are reintroduced into the product. It should also be noted that the samples with less than 50% THC were said to contain a significant amount of delta8-THC which was not included in the total THC concentration due to its separate effects. Although not directly mentioned, this probably should only include THC that has been decarboxylated, since distillate is used in the production of edibles and vape cartridges.