In states like California, drug screening remains a thorny issue, because companies must carefully enforce any drug-screening policy in a way that does not increase their exposure to employment-related tort claims, especially for invasion of privacy.

Generally, there are four types of drug testing: pre-employment screening, random testing based on "reasonable suspicion" and post-accident testing. One common theme for all types of testing is that providing employees with advance written notice of a drug-testing policy diminishes an employee's (or applicant's) reasonable expectation of privacy.