It would still go through the liver for metabolism. The only thing “boofing” effectively does is skip the stomach part of the digestive process. To take up anything from the digestive tract, it gets transported through the intestinal lumen and into the mesenteric and hepatic portal system. The liver filters everything that gets into the blood from the gut before it goes into the inferior vena cava and into the rest of the circulatory system.

Correction to clarify: the lower gut/colon mostly only takes up water and certain vitamins that are released by gut bacteria, and very small molecules like ethanol can sometimes get through as well. The very lowest part of the colon does have a vascular supply that can bypass the liver, and there are some medications designed to take advantage of the select receptors and transporters down there. However, neurotransmitters and peptide hormones (which is what OP was asking about) would likely not get taken up until it was much higher up in the digestive tract, and at that point it would go through the hepatic portal system.

Thank you to those that corrected me. Intestines are actually fairly complicated.