This story is doing the rounds today - one version in Daily Mail, another in the Express. I thought this slightly more serious and complete article appropriate to post here.
Metformin is a drug commonly used to treat type 2 diabetes by controlling the amount of sugar in the blood. Now, a new study suggests patients with under-active thyroids who take metformin have an increased risk of low levels of thyroid-stimulating hormone.
medicalnewstoday.com/articl...
Rod
Rod,
Sloppy reporting: "However, previous research has suggested that metformin could lower TSH levels, potentially exposing patients to harmful effects of subclinical hyperthyroidism. "
Low TSH doesn't mean a person is hyperthyroid but it can prevent them getting a sufficient dose of thyroid hormone to resolve their hypothyroid symptoms 
Deja-vu moment about this 'amazing' drug? closely linked diseases...
then again, I can't remember the cortisol-blood sugar connection either.
I shall consult the book of links. J 
Rod, just by chance Medscape published a study today about the Microbiota and Diabetes which said.
"Interestingly, certain antidiabetic drugs such as metformin also interfere with the intestinal microbiota."
medscape.com/viewarticle/82...
I wonder is the change in the Microbiota could affect conversion in the gut. PR
PS When the article starts off with this statement it really makes you wonder.
"Having an under-active thyroid - also known as hypothyroidism - means that the thyroid gland does not make enough thyroid-stimulating hormone (TSH) to meet the body's needs."
And all this time we thought it was the pituitary that made TSH, no wonder we have so many
problems.
I long for the old days in news when there used to be more fact checking and better editorial review.
I would not be in the least surprised if many medicines have an impact on the gut microbiota and thence the rest of us. It strikes me as a very important reason that animal trials can never fully identify the safety and efficacy and side effects of medicines. Unless they have at east very similar microbiotas the differences in this one area could be massive.
(Mind, that is not to say that suitable testing of all types isn't necessary. Even if not the full answer, it is a necessary part of the process. Just don't think you'll learn everything from it.)
Coincidences are often amazing. But sometimes we seem to find that there is a co-ordinating factor - in this case, has someone got a new generation beyond-metformin medicine they want to launch?
Rod
I don't consider myself to be good at critiquing articles - but that one was really shocking even to me!
Before I joined this forum I read of some research that was being carried out in a few cities of the UK. It was in the Sunday Times I think .... They were giving Metformin to Mums - probably overweight Mums - who were expecting in order to prevent babies being obese later in life. I was incensed and wrote to the people conducting the experiment. I still have the very patronising reply to my suggestion that they should perhaps test Mums first to see if there was an underlying thyroid condition. The reply was long and only mentioned thyroid in the last line saying they would not treat anyone with any known condition. With the TSH range of 0.5-5.0 I suspect a lot of people were missed.
beta.nihr.ac.uk/research/re...
Can't find the reply - but did find my mail. The research is in the above link somewhere around 2011. In a rush so didn't have time to search. Thought people would find the amount of research being done and the amounts of money involved interesting......
What's the cortisol connection to blood sugar?
Thyroid level dangerously low?
Low Thyroid Hormone Sensitivity Associated With Increased Mortality Risk
Low sex hormone (SHBG) and testosterone levels 
Cancer cells use thyroid hormones differently from non cancer ones
Low Vitamin D and thyroid hormone utilization connection?
