I read that it did awhile back but I don't remember where. I just say tickle because in my mind that's how it worked, I can't see why it wouldn't potentiate to the extreme extent it does or help with opioid withdrawal so much if it didn't have some affinity to the MOR.
According to
this source: "It has been proved in many in vitro studies that calcium channels/blockers modulate the opioid receptors or release of endogenous opiopeptins in one or other way."
I'm not entirely sure how to interpret that but it sounds like it at least has some involvement in the MOR. It's particularly popular for people coming off kratom, it helps with opioid withdrawal in general but it seems to help with kratom withdrawal the most.