I had been taking Mercury Pharm Levothyroxine and so requested the same brand from the pharmacist but was given Eltroxin. I then had what it seemed like stomach flu the next day(and could well have been) or possibly a reaction to the Eltroxin. Is it likely it could have been a reaction? Is Eltroxin different to Mercury Pharma? The only other difference was the strength. The MP was 25mcg and the Eltroxin was 50mcg (due to increase every other day). Has anyone else had a problem?