Hi Christophe, Zantac/Zyrtec can be very helpful in many cases of POTS and helps with difficulty standing and some feelings of weakness. It blocks histamine, which can dilate the vessels and contribute to symptoms of POTS. Most folks use a “double dose” (just double whatever the label says!). As far as human growth hormone, it may be worth it to check her current levels (IGF-1) to see if she has room to go up, if that makes any sense. HGH can help us maintain strong bones which can be helpful, especially for women. I hope that helps! 😉