Synthroid I have found has helped me with some physical issues and maybe even cognition, I was put on it this spring, only 25mcgs. I have read a lot how thyroid overactive or underactive can wreak havoc in so many ways involving almost every organ/system(s), including brain function,
Many doctors only prescribe thyroid med for hypothyroidism(slow functioning) if the various levels of thyroid hormones are not within the "normal" limits, but studies have shown that may not always be the only reason when med should be prescribed cause what is normal limits for one person may slightly vary or in my case I was on the fringe till more characteristics prompted another re-test and then it showed not within "normal" limits. I have many of my aunts,my mom and my grandmother who is 94 y.o. BTW that have been put on Synthroid and they all see a positive difference.
I had a gyn once that didn't believe in solely going according to the tests, he observed other physical features that were signs of hypothyroid, when I wasn't getting pregnant as we thought I would he said the next step was to try thyroid meds, boosting internal organ function that slight sluggishness could contribute to near inability to become pregnant.
Sorry, I got carried away, but in my opinion I wouldn't be afraid to give the Synthroid a try. I wish I could remember this website that had a psychiatrist who has done research and also uses thyroid meds often in addition to psychiatric meds and in some cases alone and the patients condition(s) improved, some turned out to only need thyroid meds.
There are some really good books about this at Borders or even other good book stores, I recently bought one printed in the UK by the Oxford press and I think the title was just Thyroid, I do not have the book close by, but can get the info you decide you are interested.
I apologize if this "2 cents" of mine wasn't of any use to you, but just wanted to assure you that Synthroid is a commonly used thyroid med. for thyroid disorders and/or adjunct to some psychiatric meds.
I wish you lots of luck with this
"darkeyes"

In giving advice seek to help, not please your friend
SOLON