I have been on generic levothyroxine since my TT 7 years ago. Last year the manufacturer switched from Lannett to Amneal but I noticed no change in my TSH. There is a tiny difference in absorption rate between manufacturers and there was one study indicating the brand name to be more consistent batch to batch but any difference is very small. Remember your body at different times has different requirements for T4, even when you had a thyroid, and this may have more of an effect than any minor inconsistency. Staying on one manufacturer, whether generic or brand, is best and you can adjust the dose accordingly. I notice a slight seasonal change (my TSH runs lower in winter), dose varies if I gain or lose weight even just 10 lbs, and of course if I have to take PPIs like Nexium, stop or start morning coffee drinking, or any of the other things that interfere with absorption. The secret is consistency. For example, if you always drink coffee in the morning, even if you wait an hour after levo, know that it reduces absorption and you may require less levo if you quit coffee. Bottom line, the generic is way cheaper (I pay zero thru insurance and it runs $12 without) and I have found it to work just fine. I have been on 88 micrograms since 6 months postop TT.