If you're trying to cut for your own supply, it is not a good idea because it is impossible to ensure even distribution in a mix of powders. You will have hot spots that will be more potent than other spots. This can lead to overdosing very easily. Pharmaceutical companies use complexes of binders in order to ensure even distribution, but that is not possible to do at home. A much better solution is to make a solution for liquid measurement. Use alcohol, vodka or something, to ensure the solution remains sterile, and dissolve it into, say, 1mg/mL. So if you had a gram, you'd use a liter. You could do it more potent too, the point is it should be a known amount... a gram into 500mL of vodka would give you 2mg/mL. Then you use an oral syringe to dose it, and you can be sure you're dosing properly to a high accuracy.
If you're trying to cut to deal fentanyl, then please don't do that, it's dangerous and irresponsible. Also see the above.
