To my understanding, neither CBD nor THC are effective for “severe” pain; rather, they work better for mild to moderate chronic pain. Often, with severe pain, the dosage of opiates can be decreased with concomitant use of medical cannabis or CBD and that decrease in dose makes their use safer. Concurrent use of THC does increase the analgesic effect of CBD, but it also adds the “high” which some people do not want as a side effect.
Then there is the matter of which part of the plant is used. THC tends to be more concentrated in the leaves of the plant, while CBD in its stem and seeds. It should be noted that these aspects are relative. Some degree of agreement exists that for the purest CBD, the stalk of a hemp plant (varieties of cannabis generally grown for fiber manufacturing, low in THC), or much less often the seeds. Taking into account the fact that CBD supplements are usually in an oil form, one may fathom the origins of the nearly ubiquitous hemp oil dietary supplements.