headaches and tanin related?

[winer]

For years I have passed on drinking red wine, because even two or three glasses would give me a pounding headache. I recently found a Chilean Merlot (which is good and CHEAP) that I can drink (within reason of course [img]http://www.wines.com/ubb2/wink.gif[/img]) without suffering any difficulties.
1. What is it in red wines that causes headaches? Is it the amount of tanin in the wine?
2. Are Merlots in general low in tanin?