Can I take letrox 100 "old line-up" and at the weekend 125 "new line-up"?

So you can apply the new composition of the drug. The change in composition applies only to excipients that should not affect your pharmacotherapy. Medicines in a new package and with a new composition should be used as you have used medicines so far. Be aware that close monitoring is recommended for patients who switch from Letrox to new tablets, as a change in composition may cause thyroid dysfunction. It may or may not be. Side effects can be reported, even should be reported to the doctor or directly: Articles that can help you understand the topic: https://www.gdziepolek.pl/artykuly/jak-i-dlaczego-zglaszac-dzialania-niepozadane https://www.gdziepolek.pl/artykuly/czy-bac-sie-dzialan-niepozadanych-lekow