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What did Jesus drink on the cross?
They gave him vinegar to drink, mingled with gall. - Matthew 27:34
And they gave him to drink, wine mingled with myrrh.- Mark 15:23

"Gall" is a general term for anything that is bitter. The Hebrew behind the Psalm word can mean poison, but also meant gall or hemlock. Myrrh was a bitter substance. Some (even Raymond Brown) deny that this is possible (though even he did not give a reason for saying so), but let's look at the original Greek word used by Matthew, chole. It's used in one other place in the NT, Acts 8:23 -

For I see that you are full of bitterness and captive to sin.

It is manifestly used in both verses in a non-technical sense of something generally bitter.

One suggestion made is that Matthew didn't know what "myrrh" was. That is doubtful. Matthew uses a different linguistic form of the same Greek word in Matt. 2:11 re a gift brought by the wise men.

But why did Matthew use this general word rather than the specific "myrrh"? Two reasons are possible.

First, because he already used the word in 2:11 to refer to a gift, and something pleasant, and did not want to invoke a contrary association.

Second, Matthew was probably engaging in a bit of typological midrash here, as he used the same word that is found in the LXX version of Psalms 69:21 - "They put gall in my food and gave me vinegar for my thirst."