Lab Testing for Purity? (in %)

[Caribbean Sky]

Is lab testing for fentanyl reliable and possible? Is it a good idea? How does it work and long does it take?

I don't have any in-person access, so I know I'll need to contact and ask for instructions via mail-in.

What are some of these labs I can send a sample to test to if its a good idea?

 

[rxg116]

I'd like to know the same for N/SN