What does someone take if they have low blood pressure?

Nothing: Blood pressure of <90/60 is considered low. Yet many, thin young women are walking around with this. If there is no sign or symptoms of diminished delivery, there is no need for any treatment. If there is symptoms or shock, then Alpha agents can be used. One could use mineralocorticoids, steroids, pressor agents.

Salt and fluids: Drink as much as possible. Eat plenty of salt be checked for diabestes, and infection. If you have diarrhea, vomiting or (if female) heavy periods, they could be contributing factors. There are rare diseases (like addison's) that can cause it. Btw, low blood pressure without symptoms is a sign of health and isn't treated!