While this decision is always left up to the individual, the chapter on the Third Tradition in "It Works: How and Why" states:

"Narcotics Anonymous offers recovery to addicts around the world. We focus on the disease of addiction rather than any particular drug.  Our message is broad enough to attract addicts from any social class or nationality. When new members come to meetings, our sole interest is in their desire for freedom from active addiction and how we can be of help."

Please review IP  #7 - "Am I an addict?" and IP #22 - "Welcome to NA". 

 You may also be interested in the Service Pamphlet, "An Introduction to NA Meetings."