Zinc and magnesium duly noted, thanks guys! How much of each do people find are necessary, is dose dependent on size at all (I'm about 105lb/7.5st/48kg), and which forms are best? I'm not on a huge dose of zinc right now, just the 9mg in my multivitamin plus another 25mg from a cheap zinc gluconate (found the bottle in the kitchen cupboard, thought I may as well use it up). For magnesium, I mess around with taking magnesium malate tablets and taking magnesium citrate powder in my electrolyte drink. Both the type and the amount depend on what my gastro-intestinal tract is up to, which in turn depends on various things but particularly what meds I'm on. Right now I'm tending towards constipation (coming off the gabapentin, possibly the B12, and having to take codeine fairly often for pain), so I can tolerate more magnesium.