In answer to the objection that urine tests reveal only very recent use of hard drugs, Bruce Reed says that before long, drug-testing technology will have advanced from urine to hair tests, which may reveal chemical traces for up to a year.
Hair tests are more difficult and more expensive than urine tests, by are more effective.
mnli hypothesis: Hair tests are more difficult and more expensive than urine tests, by are more effective. premise: In answer to the objection that urine tests reveal only very recent use of hard drugs, Bruce Reed says that before long, drug-testing technology will have advanced from urine to hair tests, which may reveal chemical traces for up to a year.