Yes, you may be denied life insurance if you smoke marijuana.

Marijuana is unfortunately considered an illegal drug in most jurisdictions so you could be denied coverage when applying for a life insurance policy. 

There are some life insurance plans you can get that offer guarantee issue with no health or drug questions on the application. Unless the life insurance requires a blood or urine test, the life insurance company would probably never know you use it unless you tell them. 

However, if you lie on an application for life insurance coverage and die within two years of the start of the life insurance policy  as a result of a drug related incident and drugs are found in your blood stream, the life insurance company can refuse to pay the death benefit.

There are some insurance 

companies that offer life insurance for marijuana smokers.