"Given that ld50 of anhydrous caffeine USP is above 100mg per kilo of body weight, I do not think a few grams, especially through skin, would be much risk."
Fine water-soluble powders are absorbed quickly when inhaled, producing a very high peak concentration in the blood that supplies the heart. If it is enough to stop the heart from beating, you die, even if dose averaged over the whole body is reasonable.
Fine water-soluble powders are absorbed quickly when inhaled, producing a very high peak concentration in the blood that supplies the heart. If it is enough to stop the heart from beating, you die, even if dose averaged over the whole body is reasonable.