Zinc and/or B12 (methylcobalamin) deficiency?
You need a homocysteine test for the latter, as the MMA test does not show methylcobalamin levels and for zinc, just do a trial, instead of testing.
Also ensure you're staying hydrated, by drinking 6-8 glasses of spring water daily.
Consuming foods containing vinegar or lemon/lime juice, induce saliva production, which will alleviate the metallic taste.
Finally, if you have some GERD symptoms (GERD might cause metallic taste), you should find out why (low or high gastric acid levels) but please do not consider anti-acids or PPIs,until you know for sure your gastric acid levels. Low gastric acid is associated with low B12. You can do on your own the Betaine HCL challenge or the baking soda "burp" test for low gastric acid .
Just look it up online
Hope this helps.
Niko
Hi what Medication's are you on if any , cause some Med's give that side effect a Metal taste , hope it helped , Take care ,