A possibly interesting article in the Guardian.
The system is also riddled with exceptions and complexities. In a historic anomaly, if you have an underactive thyroid that means you need to take daily replacement therapy, you get all your prescriptions for free. But if you have an overactive thyroid that requires drug treatment, you pay. Such issues have obviously helped persuade the Welsh, Scots and Northern Irish that it’s simply not worth bothering with charging.
It has always looked to me as if iatrogenic hypothyroidism (that is, caused by doctors prescribing carbimazole or propylthiouracil) is every bit as deserving of "free" prescriptions as hypothyroidism with any other cause. Getting that argument past someone who doesn't want to agree is another matter altogether.