When I first started using menstrual cups, I always had some leaking on my first two days, which, incidentally, were my most "crampy" days. Leaking usually occurred before the cup was full, so it was a seal issue, not an overflow. Never had leaking on my final, cramp-free days, even with a full cup.

Over the past year, I've done some major cramp and PMS troubleshooting. I didn't like taking ibuprofen all the time--it wasn't good for my stomach, and while it reduced cramping, it seemed to drag out my period by an extra day. So I tried drinking more water, changing my diet, using various herbal teas (melissa, raspberry leaf), cod liver oil, etc.

The most effective "treatment" I've tried has been magnesium supplements, which I take daily throughout the month. Over the past several months, my periods have gotten progressively less painful (and several other non-period health complaints cleared up as well), and my PMS symptoms have been reduced. Last month, I took ONE anti-inflammatory pill, and only had ONE day of using a hot water bottle. This month, I had NO pain, took NO anti-inflammatory pills, and didn't even reach for my hot water bottle.

The curious part is that the incidents of leaking (which I had already reduced by switching to soft/flexible rim cups) completely vanished, even though my volume of menstrual fluid remains the same.

Now I'm wondering if uterine cramping can cause leaking? It makes sense to me--if the rim of the cup is up against the cervix (which is where mine always wants to sit), a cramp in the uterus could potentially change the shape of the upper vagina and mess with the seal. Also explains why I got less leaking with soft-rim cups, since I suspect they are better able to move with shifting vaginal walls.

I'm curious what you knowledgeable cuppers/vagina experts think!

And also, insert-plug-for-investigating-magnesium-deficiency-as-a-possible-cause-of-painful-cramps. It seems to have been my silver bullet--I actually think I got the suggestion from this community!