As always, anything taken to excess is harmful. I use 7PPM with excellent results. At higher concentrations it tasts too metalic anyway. I eliminated my chronic sinus infections using 7PPM, so why use higher concentrations?? Years of problems were brought under control in 3 days.
P.S. Any person who takes a multi-vitamin everyday is consuming more copper,iron and other metals at a much larger partical size than I am with Colloidal.