The biggest study done on this topic which was just released a few weeks ago concluded the exact opposite, that moderate to even heavy drinking increases intelligence.
The long-term study followed a large group of civil servants (30,000) in the UK. The study started in the 1960s and has added more drunkocrats over the years.
Long-term scientific studies are more apt to produce an accurate result than a short-term test-tube study.
The study found that those who had 3 to 5 drinks per day (moderate to heavy drinking that is) performed much better in their jobs and were promoted far more often than their non-drinking soberocrats. They also performed much better on the UK civil service testing standards.
It even seemed that the heavier the drinker, the more their performance improved.
That's because they were out drinking with their boss! (grin)