From The Truth About Guns:

People use these products to treat everything from epilepsy to arthritis. Despite its popularity, it’s very important to realize anything related to cannabis triggers potential criminal liability under both state and federal law.

Many people believe that if CBD oil is legal in their state, then they have nothing to worry about. Unfortunately, this is wrong. If you want to remain a legal gun owner, you should pause before you inhale or consume any product containing CBD oil.
If you’re using CBD oil as a treatment plan or have a medical marijuana prescription, you might inadvertently become classified as an unlawful user under federal law. If you are an unlawful user, you would no longer be legally eligible to purchase, own, possess, or transport firearms.