What is the most common drug testing method?

Drug testing is one action an employer can take to determine if employees or job applicants are using drugs. Testing can identify evidence of recent use of alcohol, prescription drugs, and illicit drugs.

Drug testing works best when implementation is based on a clear, written policy that is shared with all employees, along with employee education about the dangers of alcohol and drug abuse, as well as supervisor training on the signs and symptoms of alcohol and drug abuse, and an Employee Assistance Program (EAP) to provide help for employees who may have an alcohol or drug problem.

Companies that implement employment drug testing services most commonly use urine drug screening because of its fast, affordable, accurate results. Urine drug tests can detect a range of substances, including but not limited to methamphetamines, opioids, PCP, cocaine, cannabis, and benzodiazepines. Urine drug testing can be done at your location or off-site and does not involve an invasive procedure.

The U.S. mandates drug testing for certain employers, such as transportation firms. The federal government accepts only urine drug screens for this purpose.
Some urine drug tests provide immediate results, while others take a few days. These tests can generally detect drug use within the past several weeks, depending on the substance, frequency, and other factors.

Resources:
https://www.datia.org/datia-resources/27-credentialing/cpc-and-cpct/931-workplace-drug-testing.html