The phrase "be on the edge" can be replaced with a number of synonyms that convey a person's state of being almost at a breaking point. Some synonyms for this phrase include hanging on by a thread, at the brink, on the cusp, on the verge, teetering on the brink, walking a tightrope, and at wit's end. These phrases all denote a person's emotional or mental state of being almost overwhelmed and close to breaking down. Depending on the context, the appropriate synonym can be used to add extra emphasis to the situation and convey the urgency of the person's struggles.