So I just read this: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3654245/.

I was hoping for more on activated charcoal, but there's little here and the study to which it links positively states that Cholestyramine is much more effective. No evidence cited, but everything I've read claims as much. Again, there is very little research into charcoal (for obvious reasons), but it's still worth a try, very harmless.