Finn, I don't know whether you would have access to anything like this but I'll offer it anyway. I had a urine test done called an Organic Acids Test. It was very revealing. One of the things it revealed was that I my body was deficient in serotonin, magnesium and B6.

My doc prescribed additional supplementation above what I had been taking in magnesium and B6 and then he added the amino acid L-Tryptophan to remedy the problem in my serotonin metabolism. For me it was an overnight change. My anxiety and depression and fibromyalgia symptoms disappeared.

There is another blood test called a Neurotransmitter test that will also test the neurotransmitter levels. Then you'll know where you stand and whether you might benefit from supplementing with any of them.

The labs that do these tests are elite labs and they do deal with people internationally.

The lab that does the Organic Acids Test is Metametrix. Here is a link taking you to the lab and a description of the test and it's benefits: http://www.metametrix.com/content/DirectoryOfServices/0091OrganixComprehensive-Urine

And here is a site where you can order a Neurotransmitter test:
http://www.integrativepsychiatry.net/index.php?pr=Neurotransmitter_Tests

Hope this helps!