I’m on tirz, and the first few months were rough. I started late 2023, and that’s when I started running again (after injuries). I improved slowly and upped my mileage. My heart rate was high and took time to settle. But I got better. Once I started tirz maintenance, it got easier. Eating enough carbs for training is key. Now I run 50-70km a week easily. I stop the meds one or two weeks before a race. But the longer I use tirz, the less it affects things.