Salvinorin A becomes active in micrograms. 1 microgram = 1 gram*10^(-6), right? I'm not sure how many dosages are in 1 mg, but I bet it's a lot. Be careful man, Salvinorin A is extremely potent (I think it's the most potent psychedelic).
One mg is 1000 ug(microgram) 1mg will rock your socks off . It is a little less than Daniel Siebert's Eureka! Trip report, the first use of pure salvinorin. If you ask me, thats pretty damn expensive, as it is actually only a few rides. For that price you could make you own pure salvinorin fairly easily and yield quite alot more. All you need is salvia, quality acetone or ethanol(Everclear)(my personal choice due to low toxicity and known purity), and 90+% isopropyl alcohol(rubbing alcohol). All of this can be purchased for just a few dollars. The process is simple. Its really not that hard to do in your kitchen Kids please do not attempt chemistry in your kitchen without adult supervision Witchdoctor