"Someone must have blown cocaine up my nose while I was sleeping."

"I only handled the cocaine. I didn't actually use it."

"I must be positive for cocaine because I drank Coca Cola."

"I got a DUI because my taillight was out."

Those are a few of the excuses and denials substance rehabilitation personnel at Greenbriar Treatment Center have heard from abusers after they have gotten caught and sent to rehabilitation.

Sometimes the excuse seems legitimate, only until its repeated over and over.

"Reporting four flat tires in a month" is one favorite, Judy Shannon, director of community and corporate services, said at a recent seminar on drugs in the workplace for supervisors. "Grandmother dies repeatedly is another."

Another time, Ms. Shannon said, a supervisor realized that users were turning in excuses for absences that read the same way and were signed by the same doctor. They had been downloaded from "myexcusedabsence.com," a Web site from which buyers can obtain excuses, supposedly for entertainment purposes only.

But there are other tip-offs that supervisors should be trained to look for and document.

"They can look for changes in behavior, absenteeism, errors. They're argumentative," said Dr. Neil Capretto, medical director for Gateway Rehabilitation Center. "They appear impaired in some way."

Other signs of substance abuse, as illustrated in a slideshow given at the Greenbriar workplace seminars:

• Tardiness and absenteeism, sometimes with peculiar patterns, like the day after payday.

• On-the-job absences coupled with such things as trips to the parking lot or restroom.

• Variations in job efficiency, such as missed deadlines or bad decisions.

• Concentration problems.

• Changes in attitude and/or morale, including wide mood swings, loss of enthusiasm or humor and loss of pride in one's job.

• On- and off-the-job accidents or mishaps.

• Attempts to borrow money from fellow employees or to get advances on wages or expense accounts.

Gateway and Greenbriar advise businesses to have drug policies in place to cover the legality of employment assistance programs and drug testing programs.