There are many reasons a person might fail a background check or otherwise be barred from purchasing or possessing a firearm. Below is information about some possible reasons. For information about restrictions on convicted felons, see the felons and firearms page of this guide.
Under the restrictions of the federal Gun Control Act, it is illegal for a person "who is an unlawful user of or addicted to any controlled substance" to possess, receive, or transport firearms or ammunition. This has raised concerns that participating in a medical marijuana program may cost patients their rights to possess firearms. However, the Texas Department of Public Safety has stated in an FAQ that they do not believe participation in the state's CUP program disqualifies a person from possessing a firearm or obtaining a Texas License to Carry, although it's possible that a patient's underlying condition may disqualify them.
The following links provide more information and context but do not yet address how Second Amendment rights may be affected by the use of CBD or hemp-derived products as that is still a developing area of law.