Some states like California, where Rogan's podcast is recorded, have legalized the plant for recreational use. However, marijuana is still illegal according to U.S. federal law. U.S. Attorney General Jeff Sessions rolled back President Barack Obama-era policies in January that previously dictated the Justice Department would not pursue cases against those who violated federal marijuana laws in states where pot had been legalized.

Tesla also asks that you do your part by following safety and health rules and practices and reporting (either openly or confidentially) accidents or any unsafe equipment, behavior (such as use of illegal drugs) or conditions to your manager, supervisor, Human Resources or the Legal Department. Violence and threatening behavior are not permitted, and under no circumstances should you bring a weapon to work. Employees should report to work without being under the influence of illegal drugs or alcohol. The use of illegal drugs in the workplace will not be tolerated.

One could argue Musk was representing Tesla as its CEO during the interview. By imbibing alcohol and marijuana, he was "under the influence" while at work.

In an email to The Guardian, Musk said, "Our policy allows trace amounts of THC [an ingredient of cannabis] during work times, provided they are below the safety limit (much like a minimum alcohol level)."

This isn't the first time there's been concern about Musk's drug use. Tesla board members have also raised concerns over Musk's consumption of recreational and prescription drugs, according to The New York Times. In particular, sources told the publication that Musk's use of sleeping aid Ambien may be having a negative effect, causing him to ramble on Twitter.

Tesla did not immediately respond to a request for comment. The company's shares were down as much as 9 percent on Friday morning and closed down 6 percent.