Have not read the research on black seed oil, but I will mention that it is exactly the type of supplement that has a very high chance of being dodgy if bought on amazon, newish fashionable or expensive.
The one compound that is reasonably available with really very good evidence, by any standard and amazing for a supplement where the research is usually very thin to put it nicely, is PEA or palmitoylethanolamine, with a few hundred studies showing it reduces chronic pain and unusually works slowly and increases in effect over 4 to 8 weeks. Not super cheap and I think 90% of the ones on Amazon US are dodgy, one had pills that weighed 300mg despite advertising 1450mg per capsule. Maybe iherb, micronised is preferable. Liposomal would be good but as far as I can tell every single brand advertising this is dodgy. Plain PEA needs 2-4 times the dose of 600mg x 2 micronised version. It did not fix my chronic gut pain from ulcerative colitis/ IBS-d as much as I hoped but helped with chronic pain from a sensory peripheral neuropathy.
The level of scientific evidence supporting its use for chronic pain is in a different league to any of the peptides, and oddly it has no known side effects.