While many states have passed medical and recreational marijuana laws, using marijuana is still illegal by federal law. Additionally, certain jobs may require that employees refrain from legal and illicit substances for optimal performance. You can require that employees take pre-employment and post-employment drug tests; however, you should communicate testing requirements clearly before and after hiring. In most cases, testing is limited to heavily regulated positions such as truck drivers and pilots. Most include testing information in the employee handbook and require the employee to sign in agreement with the company policies. Some have claimed workplace discrimination when being reprimanded for medical marijuana use, so you need to be careful about testing requirements. To help you navigate your state's marijuana laws, you may benefit from consulting with an employment lawyer.