Following is a sample of a warning you might see on a bag of lithium:
"By OSHA definition, lithium carbonate is not an acutely toxic chemical, but accidental inhalation or ingestion of large amounts (more than a few grams) could cause tremors, nausea or, in extreme cases, fatality. Avoid inhalation of nuisance dust containing lithium carbonate to avoid respiratory impairment. There is a slightly higher than normal risk of birth defects among pregnant women on lithium carbonate therapy (about 1000 mg/day), but there is no evidence of such effects at lower levels. Nevertheless we recommend that pregnant women be excluded from processes where exposure to lithium carbonate is in excess of 5 mg/m3."
The prescription of lithium carbonate is wide spread (at near toxic levels for manic depression). It value relates to its substitution for sodium in the conveyance of brain signals. Many studies have been done on the side effects (i.e. skin disorders, kidney dysfunction, nervous system damage, birth defects). The blood levels considered therapeutic for some people are supposedly toxic to others. Since so many people are on precisely controlled lithium therapy there is a risk involved in using glazes that leach additional lithium into these people's systems. Thus there is some need for caution about providing additional sources.
Lithium carbonate is slightly soluble in water (one gram dissolves in 78 ml cold, 140 ml boiling water).
However there are also those who hold that leachates from glazes are not enough to be significant. The subject of lithium toxicity has often been dealt with on the Clayart discussion group on the internet and the whole spectrum of opinions have been represented (with well informed people on both sides). Even people on lithium therapy have contributed and claimed that symptoms of toxicity are very evident and there is ample warning before toxic levels are reached.
Here is one guideline: The usual dosage used to treat patients with bipolar disease is 150 to 600 mgs three to four times per day (maximum amount being 2400 mg per day). Also, do not underestimate the amount of metal a very unbalanced glaze can leach (i.e. 10,000 ppm has been documented).
Lithium Carbonate at ilo.org