I tried cinnamon, but did not find it had any detectable effect on my numbers or how I felt. I tried several other OTC things, the names I don't recall, with similar lack of success.
There was one that helped. I used chromium picolinate for about the first 2 years after I was diagnosed, and then it lost effect. The way it works is to help your body use the insulin it is producing more efficiently; e.g. lower the body's resistance. I did notice an improvement in my numbers and how I felt when I was on it and it was working, so I would say it is worth a try and see how it works for you. YMMV.
The little known fact (among many type 2 diabetics) about type 2 diabetes is that it is progressive, and eventually the insulin resistance that is your initial problem (but the body is still producing lots of insulin) may/can turn into a loss of the body's ability to produce insulin in the first place. The exact reason for this effect is, to my knowledge, unknown. In my case, my body lost over 90% of its ability to produce insulin, so no matter how "efficient" the use is, there was not enough to go around.
The speed and severity of the progression is very individual, and a person can improve if diagnosed early, and/or hold the progression at bay for years by doing the right things. But it is still a lifetime condition.
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"Better is the enemy of good enough."