Hi,
Given that you are both UK State Pensioners, you need to talk to the UK Pensions Service in Newcastle (Tel 0191 218 7777) about obtaining E121 coverage for healthcare over here.
Once you are over here you should register with the Spanish Social Services at the office closest to your Spanish address using the E121 form.
Enquire at the same office about registering with a local doctor.
Prescriptions are free to people registered as pensioners. Thyroxin is available but may well be stocked under a different name. So bring with you the packaging of the UK product. Same goes for any UK medicines. The product supplied might not be exactly the same but will be the closest equivalent available. HRT products are an example of this.
A lot of products which require a prescription in the UK are available over the counter without a prescription but obviously you will pay the normal price.
You might also like to take a look at this website which is Age Concern in Spain;
http://www.acespana.org/
There is also a wealth of information published by the UK Foreign Office about Living in Spain, see this website…
http://ukinspain.fco.gov.uk/en/
Hope this helps…
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