Or, instead of using some artificial chemical to get the flavor of sassafras, you could just BUY real sassafras:
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Googling for "sassafras price" will bring you many alternatives.
As usual, you can also find it on Amazon:
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Also, if you want the hints of anise and wintergreen that dihydroanethole has, better brewing supply houses carry anise and wintergreen (I can even get BOTH of those spices at my local Fred Meyers in the natural food section).
Why in the world would you want to buy a chemical used extensively by perfumers and the tobacco industry to "flavor" cigarettes in your brew?