Short translation from Japanese to English...

Could anyone help me translate this phrase from a wooden cylinder like container. It belongs to my uncle who is very curious as to what it might say. The man that gave it to him said it had something to do with opium trade (which I highly doubt as the man also said he picked it up in Vietname - when the writing is Japanese). I don't speak any Japanese myself but, after some research, it appears the first three characters are katakana for "me" "so" and "nu" (though I have no idea what that means). The last character appears to maybe be kanji and I had absolutely no success in tracking it or a radical down. If anyone could help me with this, I would sincerely appreciate it. Thank you for your time.

http://img96.imageshack.us/img96/3586/p1220981.th.jpg

Once I posted reply to you but it seems it was deleated by the technical problem...
It is "メンタ酒" and is read as "ME - N - TA - SAKE"(not me-so-nu) which means "mentha-alcohol".
I don't know what it is but it seems to be drunk as a kind of medicine.