In recent years, perhaps decades, there has been evidence that growers of cannabis (marijuana) have placed an effort on creating strains which have elevated levels of THC and decreased levels of CBD than were typically found in nature.
Additional studies such as this one, have indicated that unwanted psychological effects can occur from the elevated THC found in some marijuana. At the same time, this study found that pre-treating with CBD inhibited psychosis symptoms from THC as well as decreased cognitive impairment.
As MMJ In The USA has reported before, such as here, here, and here, medical marijuana is often effective at low dose THC with appropriate levels of CBD still remaining in the whole plant medicine.
Medical marijuana users differ from recreational users in that they often choose to start with low doses, increase slowly, use the least amount needed to get the therapeutic effect, and use product with more balanced THC to CBD ratios.