There are many different thyroid hormone replacements in the world. There are branded replacements and generic replacements (generics are copies of the original drug). They come in tablets, capsules and liquid form. Some are lactose free and you can also get some with minimal inactive ingredients. Some are synthetic and some are made from the glands of pigs.
Some people find one particular brand or generic better for them than another, probably due to an intolerance to one of the inactive ingredients.
Some patients have found that when a pharmaceutical company changes the ingredients in a thyroid hormone replacement, they start to have adverse effects or that their symptoms return such as when Merck substituted lactose for mannitol in their levothyroxine in France -(http://www.sciencemag.org/news/2017/09/france-brings-back-phased-out-drug-after-patients-rebel-against-its-replacement)
We would urge any patients having side effects from any brand of levothyroxine to contact the MHRA and make a report via their Yellow Card Scheme.
Thyroid UK has put together a document with all the information you need about many thyroid hormone replacements including the manufacturers’ contact details should you need to contact them about adverse effects or supply issues, and ingredients which you can find here.