https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2771041#:~:text=Conclusions%20and%20Relevance%20Initiation%20of,effective%20as%20brand%2Dname%20levothyroxine.

Comparative Effectiveness of Generic vs Brand-Name Levothyroxine in Achieving Normal Thyrotropin Levels
JAMA Netw Open. 2020;3(9):e2017645. doi:10.1001/jamanetworkopen.2020.17645


Quick history lesson- levothyroxine was cleared and approved for generic use in 2004 – until then Synthroid had enjoyed a huge market share. The only market share. They were it and there is soooo much money when you are the only drug on the market and the most prescribed drug on the market—in 2002 the revenue was estimated at 1 billion dollars.

I was alive in 2002 and I can tell you back then 1 billion dollars was a lot of money.

But then 2004 there is now competition, a generic drug.! What does the drug company do? Use some of their small fortune to trash the drug, pay of some doctors to write a paper and later in 2004 there was a paper released by The Endocrine Society released the paper citing concern for the generic drug and the bioavailability.
https://www.endocrine.org/advocacy/position-statements/bioequivalence-of-sodium-levothyroxine

as recent as 2014 the
American Thyroid Association guideline specifically recommends
“Switches between levothyroxine products could
potentially result in variations in the administered dose and
should generally be avoided for that reason”

Meaning don’t have them on brand name synthroid and then switch them to generic. Stay constant!

But todays study wanted to look at the comparative effectiveness of generic vs brand-name levothyroxine in patients initiating therapy for hypothyroidism

4570 patients initiating therapy with thyrotropin levels ranging from 4.5 to 19.9 mIU/L were 1:1 propensity–matched

One group was started on generic levothyroxine and the other group was started on brand-name levothyroxine also known as Synthroid.

As an outcome they looked at three different things
the numbers of individuals who attained a normal thyrotropin level within 3 months,
the clinically meaningful abnormal thyrotropin level within 3 months
the number of people with stable thyrotropin level(s) 3 months AFTER having a normal thyrotropin level

Among 4570 propensity score–matched patients those that received generic levothyroxine had a normal TSH 75.4% of the time and those that got brand-name levothyroxine had a normal TSH 76.9%
And in both groups about 4% of the individuals had a markedly abnormal TSH level (94 [4.1%; 95% CI, 3.4%-5.0%] vs 88 [3.9%; 95% CI, 3.1%-4.7%]; P = .65).

They then took the individuals who had a normal TSH at 3 months and propensity matched those individuals to 3 MORE months and the proportion maintaining normal TSH levels during the next 3 months was similar regardless if you received generic or brand name levothyroxine, 82% vs 83% respectively. (427 [82.6%] vs 433 [83.8%]; P = .62).

Here is the kick in the pants-
Per good RX

Levothyroxine is $4 on good RX
Synthroid is $45