My endo initially prescribed Invokana, which I was on for about 8 months. The pros were that it immediately reduced my insulin needs by about 25% and I lost about 15 pounds quickly and maintained. I was able to tolerate the slightly more frequent urination, but there were some more significant cons which swayed me to discontinue. I experienced pretty severe dehydration the extent that I would wake up several times a night with dry mouth and had to drink lots of water. Not that I drink alcohol excessively, but I could not drink more than 1 glass of wine because the combination of Invokana and alcohol exacerbated the dehydration to the extent that it was intolerable. Most importantly it caused me to have moderate ketones twice despite BGs in the low 100s. This is what the FDA warns against. I did not go into DKA, but did have to call out sick from work for the first time ever related to T1D in order to monitor and I felt like crap. After the second time, I decided to stop Invokana.
Then my endo prescribed Metformin, which I love! My insulin needs slightly increased from the Invokana, but still an overall decrease of about 15-20%. I gained some weight back while titrating, but have been able to lose it and maintain the 15lb weight loss. I think the best part is that it really helps control my appetite. I have had T1D since I was 5 (the Lente/NPH/R days, prior to fast acting insulin and MDI) and as a result believe that my brain/body never developed hunger/satiety cues. That’s another topic, but it is very satisfying to be able eat when I’m hungry and stop when I’m full. I did experience GI symptoms while titrating, but it was tolerable. I also follow a low carb diet most of the time.
My endo was very open to trying both, which I am thankful for. I would also agree that you might consider changing endos. Happy to answer additional questions.