Coke often gets cut with other much cheaper drugs that will simulate some effects of cocaine (such as numbing) so that users are less likely to realise how cut

Coke often gets cut with other much cheaper drugs that will simulate some effects of cocaine (such as numbing) so that users are less likely to realise how cut their drug is. (All coke will be cut at least somewhat, but if you're buying it you're hoping a.) fairly high purity and b.) cut with non-toxic non-drugs, rather than other drugs) I'd be surprised if that didn't happen all the time with heroin too, though if heroin doesn't provide a numbing feeling then there's no motivation to specifically add a cheap numbing drug.. but numbing could well be an accidental side-affect of something that was added to dilute the % of heroin in each gram sold?