Thank you very much guys. Pardon the delay in my seeing this.
As it happens I did some digging and tripped over much of the material you guys very kindly have posted - and so have proceeded cautiously.
It seems in my case that it may be somewhat self limiting anyway - in that I can comfortably tolerate 2,000mg daily if crushed and taken in water, but more upset the gut.
It seems to have a noticeable effect in terms of reducing my blood pressure, probably by reducing my cortisol levels. I could push a little/try to build tolerance - but anm inclined to be cautious pending the outcome of some other options.