Facts About Drug Screening

Updated April 17, 2017

Drug screening is a common practice in the workplace, the courts and even in the home as testing, and the desire to find ways to evade such tests, are becoming more sophisticated. Today, drug screening is standard practice for most employers who generally require a pre-employment drug urine test. Random drug screening and post-incident testing, such as after an accident or police-involved shooting, also are administered.

Testing Procedures

Hair testing is becoming rapidly popular among employers and within judicial system for its accuracy and longevity. A hair sample can trace drug use to at least 90 days. Hair testing can also detect alcohol abuse. Saliva, sweat and urine testing also are common with varying degrees of accuracy.

On-Site Testing

Employers can contract with drug testing companies to come to the workplace and conduct urine drug testing on employees with results returned within one minute if the test is negative and up to five minutes if drugs are detected.

Environment Testing

Some private companies offer surface drug detection wipes in which a person's work or home environment can be tested for the presence of drugs. Cocaine wipes are the most common in which a postcard size swab is wiped on the surface of furniture or the hands of a person. Cocaine is present if the wipes turn blue.

False Positives

False positives are common and are caused by numerous medications and types of food. Medications that could create a false positive include Accutrim, Aleve, anti-anxiety pills, antibiotics, B2 vitamins cough medicines, Dimetapp, Tylenol, Vicks, Midol, Motrin and many others. People suffering from liver disease or infection or have eaten poppy seeds also could spark a false positive.

Detection Periods

The standard pre-employment urine test can detect alcohol use up to 24 hours; methamphetamine, marijuana and cocaine up to five days; heroin up to four days and PCP up to one week. Other drugs, such as LSD, also can be tested, but are rarely administered.


There are many kits on the market today that promise to mask or negate a urine drug test. However, as drug testing has become more sophisticated, such as hair samples, it is becoming more difficult to beat a test as employers also use urine adulteration testing. However, adulteration testing has not kept up with the proliferation of more sophisticated masking kits. The best way to beat a drug test is not to take drugs. The second best, and the cheapest, is to drink 2 litres of water to dilute the urine sample.

The Law

It is legal to conduct drug tests in the workplace. President Reagan signed the Drug-Free Federal Workplace executive order, which was followed by the Drug-Free Workplace Act of 1988 that made it legal to test federal employees. Those laws made it legal for private employers to conduct drug tests. But random drug testing remains a grey area due to privacy concerns and search and seizure laws and has spawned many lawsuits.

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About the Author

Rob Wagner is a journalist with over 35 years experience reporting and editing for newspapers and magazines. His experience ranges from legal affairs reporting to covering the Middle East. He served stints as a newspaper and magazine editor in Saudi Arabia and the United Arab Emirates. Wagner attended California State University, Los Angeles, and has a degree in journalism.