Which of the following is NOT a cause of hypotension?

Excessive hydration is not a cause of hypotension. In fact, it generally leads to an increase in fluid volume within the circulatory system, which can support or elevate blood pressure rather than diminish it. Blood vessels may expand in response to the increased volume, creating more pressure within the system. While there may be circumstances in which excessive hydration can lead to complications (such as fluid overload or heart failure in susceptible individuals), acute hypotension is typically not a result of this condition.

When considering other options, medication overdose, shock, and blood loss are well-known factors that can cause a drop in blood pressure. Medication overdose could result in cardiovascular effects that inhibit the normal function of the heart or blood vessels. Shock encompasses various conditions where there is inadequate perfusion to the tissues, leading to hypotension, and blood loss directly reduces the overall blood volume, thereby lowering blood pressure.