i never tried and i will never buy any illegal things with bitcoin because there is a big posiblity that you will get caught, the government knows that there are a lot of transaction on the deep web that is happening, this transactions are not easily tracked, even those who are doing illegal things will not buy using bitcoin this time because the market is so cheap, maybe if the value will get higher, even things that is legal i wont buy with bitcoin for now, i would rather use fiat money to buy the things i need.