If you test positive for any illegal drugs, you will be rejected for your life insurance application.
However, if you have a legal prescription for medicinal marijuana in a jurisdiction where marijuana is legal, then you may not be declined for the life insurance coverage. it depends on the insurance company and their position on whether they will insure someone who smokes marijuana.
Here's how you can learn more about life insurance drug tests and learn about life insurance plans that offer up to $500,000 of coverage without any drug tesst or physical examination.