I did, and got a letter back saying they were updating my medical notes but I did not need to inform them. It’s more courtesy than anything. My employer at the time (DHL) advised me to keep the letter on me in case questions were ever asked at a checkpoint.
Be aware (just off the driving topic) that metformin can cause upset stomach /dioreah, which can be a bit problematic when you’re stuck on the road. It doesn’t affect everyone and the doctors can give a slow release version that is supposed to help control this. But if it starts causing problems, talk to your doctor. Oh, and make sure you keep to your annual check ups (retinopathy, podiatry and blood tests). I’ve just found out, I’m starting with retinopathy, something you won’t know about unless you have your annual checks.