All mammals have an endocannabinoid system (ECS). The ECS was recently discovered, I believe in the early 1990s, and is not well understood because of restrictions on researching cannabinoids. The ECS is similar to the endocrine system, which produce hormones to regulate bodily functions.
All mammals produce endocannabinoids naturally. Some plants, notably cannabis, also produce phytocannabinoids. These are the exact same molecules, just synthesized by plants. Over 110 cannabinoids have been identified.
The ECS regulates homeostasis at a cellular level. CB1 receptors are primarily found in the brain, nervous system and other organ tissues. CB2 receptors are primarily associated with the immune system, and seem to impact such things as inflammation. CBD, THC, CBN and other cannabinoids seem to affect these receptors, but again science is lacking as to exactly how, thanks to our anti-cannabis bureaucracies.
In response to your question, the best control group for testing placebo effect are animals, which simply do not respond to placebos. Anyone who owns pets and has given them CBD for anxiety, seizures, pain, inflammation, nausea etc. will generally speak to the positive benefits.
A majority of people who turn to cannabis products as an alternative to prescription medications also find them effective. A recent study by Brightfield and HelloMD revealed:
CBD is most commonly used to treat insomnia, depression, anxiety, and joint pain.42 percent of CBD users stopped using traditional medications and now use cannabis instead.80 percent of CBD users found CBD be very or extremely effective for treatment.90 percent of those surveyed said they would buy CBD-only products derived from marijuana.
Considering all of the unknowns, you ask a fair question. But I think we’re quickly learning that the benefits of medical cannabis and specific cannabinoids are indeed real.