[sfem]

PM does affect your circulation in subtle ways. I speak from personal experience. How that effect affects you is not so straightforward. In my case, it causes severe numbness type pain in the ends of my three middle toes, and increases the likelihood of pain in the balls of my feet, which tend to hurt from spending too much time barefoot on hard floors (not, not in the kitchen for the misogynists in the crowd). If you have some sort of circulation impairment in your back which has not been noticeable in the past, long-term PM use at higher doses can trigger it to become noticeable (e.g. starving muscles of necessary blood flow). Simply cutting back to a minimal intake can reduce the effect to a tolerable level for me, stopping completely really improves things. I'm not very happy about it, because it really makes me wonder about other long term effects of circulatory changes from PM. I guess in a few years, I may be able to report on that if I don't find something other than PM to try. I will also say I never had this effect before the R1 version, but that may be a red herring, as it might simply be that it took a few years to accumulate enough change in my feet/toes to be noticeable.
It is very simple for you to determine if PM is causing/exacerbating your back pain. Stop taking it, changing nothing else. Give it enough time to clear your body, say a week or more, although the change may happen quicker than that. In my case, when my feet are really bad, I find an improvement in my feet the next day, and significant improvement within 3 days. The boobie fairy might punch JustEmily in the chest, but she stomps on my feet. Maybe she jabs you in the back. These aren't commonly reporting side effects of PM and it has a very long history of use, so I suspect it is related to the high dosages we subject ourselves to over longer periods.

Edit: very strange. I wrote k i t c h e n where it says tractor above. I go to the quick edit, it still shows kitchen. I cancel or save and it says tractor. WTH???