I don't think there is a maximum dosage of Inositol, though it can cause digestive problems in high doses (mostly mild indigestion, diarrhea, and gas, but you should double check this). As Mark said above, there are double0blind controlled studies showing that Inositol can help to treat depression, anxiety, and OCD, though very high lefels are required. For anxiety and OCD, you need around 18 or 20 g/day, while for depression I think the number is closer to 9g/day. To take it in these quantities, you need to buy the powder, which isn't cheap. Capsules come in much smaller doses, like 500mg, and you can get Choline/Inositol combo capsules. I don't know what sort of dosage is considered therapeutic for treating brain injuries.

I'm not sure about PS. I've been taking 100 mg/day and I think it has helped with memory and mental clarity. I'm going to try increasing my dose and seeing if it helps more.

Pete