I believe it's the doctors who are checking certain stuff when you do the blood and urine tests.
My wife went in for medical check and the result came out with high blood sugar level. The doctor's assistant called us and asked us to come in again for a 2nd test because, if they send the medical result as is, it will not look good at CIC. So we had to go in again.
If they are saying high blood sugar level could affect CIC's decision, drug in your urine will definitely affect in their decision.
If you want to do anything "recreational", you'd better do it after this process is done.