You mean like cocaine or heroin? Yeah, no one has any of that or trades in it. Believe me, drugs have an established street value which is its market value. Like gold and silver, it changes daily but that's the market.
Illicit drug transactions, by volume of product and trading frequency, are minuscule compared with all other goods and service transactions. The visibility of gold when used for all transactions would be virtually impossible to conceal. Are people really going to risk losing their gold stash, property and being incarcerated for their weekly shopping runs? My point being how fungible is it if it is illegal. That dramatically reduces the market. Gold would likely sustain a similar reduction in marketability.