I don’t want to spoil anything for you, but ethanol is actually a very reactive molecule — and in some ways, it acts similarly to opioids like heroin. It, among other things, stimulates endogenous opioid pathways, leading to the release of β-endorphins and activation of mu-opioid receptors. So, alcohol works indirectly, heroin directly – but both enhance opioid signalling. If you’re curious, this study explains it really well:
https://pmc.ncbi.nlm.nih.gov/articles/PMC3728478/