Well, first what he can do is stop his cycle, if it's not an option the best supp. is Twinlabs "blood pressure control" Starts working in a few days. Check out "swap meet" section,I'm trying to sell few of those, but I'm leaving tomorrow for 2 weeks, if you'll get a hold of me today, I can ship it tomorrow morning.
Hawthorn berry, celery seeds another option but it takes too long to start working.
He can try to control water he holds by using AI or lower doses see if that helps.