Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. The normal and expectable blood pressure range is from 90 to 120 systolic, if there is no other health issues. However, day-to-day variability is common. This value is not a very hard and fast one, especially if readings taken once or twice. Your BP of 87, can well be a normal as well. I would advise you check your blood pressure for a few days on different times of the day and if the average is still low, then you should see your doctor. Blood pressure get low with some medicine, with loss of fluid from body, like loose motions or excessive sweating, but this won t be permanent. I would advise you should take more fluids with less salt intake and keep checking your BP readings. If still low, then you should talk to your doctor to know the cause of low BP. Most of the times low BP is not very serious (if otherwise ok, like if no syncope, etc.) and may be normal in young females. Hope I have answered your query. Let me know if I can assist you further.