It's been demonstrated in a clinical setting that the presence of certain cannabinoids can modulate the effects of others, including their psychoactivity.
From what I remember of the literature, when the ratio of CBD to THC is 40:1, the psychoactivity is completely nullified, but the pain relieving and anti-inflammatory properties are preserved. CBD and THC are two cannabinoids out of 40+ the plants produce, we know very little about the others.
Unfortunately, there is no plant in existence that produces CBD and THC in a 40:1 ratio. Most strains produce between 5-22% THC, but even the "CBD rich" strains won't go higher than 10% CBD content. The vast majority of available cannabis strains produce less than 1% CBD. Clinical trials administer the exact dosages via drops, which are prepared with specialized equipment in a lab. In those cases it's easy to give someone 40 drops of CBD and 1 drop of THC and test the ratios exactly. For most patients, even those with access to the best dispensaries, we're still a few years (if not decades) off from perfecting cannabinoid therapy in that way.
Your past experiences with cannabis may not be indicative of how you'll feel with other strains. As I said before cannabinoids all have different chemical structures and all play different roles, from regulating peristalsis to sleep patterns or how hungry you should feel. Different strains produce cannabinoids in different amounts and different ratios, so if one made you feel paranoid or unwell, another might make you feel the opposite.
Cannabis cannot handle all kinds of pain, it still relies on the endocannabinoid system to act, and certain neuropathies completely bypass it. Narcotics and opiates will always be more efficient at treating pain, so cannabis is not a wildcard replacement for all pain meds.
That being said, any pain caused by an inflammatory or immune problem will be greatly helped, if not cured, by a sustained cannabinoid therapy. To make a difference on the long term, cannabinoid therapy has to be a daily regimen, otherwise, it remains a palliative treatment option.
I maintain my pancolitis in remission exclusively with cannabis tinctures I take every day, which is about as inconvenient as taking a pill. Sure beats getting remicade infusions every 8 weeks for half a day.