I went back to some notes I made in January of this year - I was planning on alternate daily fasting and felt that continuing to take my prescribed Metformin on an empty stomach may be unwise, but I wanted to be sure about the safety of doing anything other than continuing what I'd been asked.
It's interesting, because I read these notes now, copied and pasted from medical journals on the effects of Metformin - I realise how much more I understand now - or put the other way; how little I understood then about what I was taking notes on. Some of it I think I was right about, but some I was completely upside down on, because Metformin's effects are all over the place - in the most obvious way, it acts against Glucagon (suppressing the breakdown of glycogen and - separately - the creation of new glucose) but also it acts to break down fatty acids in the liver - which is partly what Glucagon does - it's really the primary benefit in fasting to reduce fatty liver.
I think it can best be described as "mis-directing" the liver - it just messes with some of the signalling so that the liver may want to do things under hormonal control but doesn't receive the instructions.
But I still come down on the same side - this is a complicated, delicate dance that our bodies go through to remain in balance - Metformin is demonstrably effective at reducing blood glucose, but it plays havoc with all that subtlety, and if you do not absolutely need it, you have to be better off letting your body control the dance, in the longer term.
Lest we forget - we don't actually know all the ways that metformin works. It's a natural remedy at heart, it's clearly effective and has the fewest side effects (I'm not anti-metformin as a remedial whatever) - but anyone who tells you how it works - they cannot know the whole story - at the very least - it mainly affects the liver in a way that's mostly like suppressing Glucagon (ie, looks like boosting insulin) - but it's a leap from that to saying it reduces insulin resistance - which is ultimately a whole-body issue with chronically elevated insulin and cellular-level changes in the way that the cells interact with insulin.
For example - breast tissue - in the presence of elevated insulin, express more glucose transporters. They effectively become "more hungry" for glucose, and that increase in glucose uptake can lead to toxicity in the cell, and this relates to the increased risk of breast cancer - it's all directly related to insulin and has zero to do with metformin. There are countless other examples like this, where reducing your insulin is preventative, but reducing your blood glucose via medication only reduces your blood glucose, and leaves you at risk to the underlying issue.
This is why (in my opinion) - the long term health outcomes of diabetics (speaking globally, in statistical terms) are so poor, and why the control of blood glucose is not the primary thing to focus on - only the easiest.
If you understand that "pre-diabetes" was referred to as "insulin-resistant syndrome" not too long ago, you will understand that in my view, in some ways it's more important for people to get this (this being the idea that allowing your body to work properly through changes to lifestyle are better than changing symptoms by medication) before they are diagnosed with diabetes, because once the pancreas starts struggling, it's so much more difficult.