The most common and most likely answer to this crossword clue is the 7 letter word SWIGGED
I've seen this crossword clue in Financial Times
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More clues leading to the result SWIGGED
Buddy explains!

The straight part
We know that "Gulped down" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gulped down = swigged.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SWIGGED mean?
SWIGGED verb- To drink (usually by gulping or in a greedy or unrefined manner); to quaff.
- To suck.
- To take up the last bit of slack in rigging by taking a single turn around a cleat, then hauling on the line above and below the cleat while keeping tension on the line.