My son is on methodone at 40mg per day . I believe he is using again, not sure about the heroin but definitely crack cocaine or cocaine . As he’s on methodone substitute would this interfere with the readings , and would it show positive for heroin even if he wasn’t using it as this is opiate based as is methodone . At my wits end and do t know what to do , I just want the truth from him . Any advice would be much appreciated thankyou