Usually after a second interview, or even an offer, but before the date of hire. The length of time that any substance is retained in the body and can be detected in the urine varies with the drug and the individual. Retention time for marijuana, for example, can be anywhere from five days to several weeks. Some employers include statements, information, or questions about drug and alcohol on their application forms. Others will advise applicants in the initial interview that drug screening is required.
Some employers make no mention of drug testing in advance.
Because a positive test result may be detrimental to your chances for employment, company policies differ. Where urinalysis is used, immediate retesting to detect false-positives may be routine. Or, retesting may be allowed 30 days later. On the other hand, some employers take a hard line approach. They refuse to retest and will reject applicants on the basis of one positive test.