It is widely accepted in the medical community that a low blood pressure for an adult is anything below 90 systolic. There is no definition of “dangerously” low pressure. however, any symptomatic hypotension should be looked at by a doctor. Go to an ER or see your general doctor as soon as possible if you’re feeling dizziness or lightheaded or if you’ve experienced syncope. Thanks, Roy.

What is dangerously low also depends on the size of the person and their normal blood pressure. If you have a patient whose regular BP is 100/60 you wont be as worried when they go down to 90/60 as you would be with a patient whose norm is around 140/85.