Dehydration: This is often the most common and straightforward cause of orthostatic hypotension, as it leads to a decrease in blood volume, which in turn reduces the amount of blood returned to the heart, resulting in a drop in blood pressure upon standing.

Autonomic Dysfunction: Conditions affecting the autonomic nervous system, such as diabetes, can impair the body's ability to adjust blood pressure in response to changes in posture.
Medication Side Effects: Certain medications, including diuretics, beta-blockers, and certain antidepressants, can cause orthostatic hypotension as a side effect by either reducing blood volume or interfering with the body's ability to constrict blood vessels.
Blood Loss or Anemia: Significant blood loss or severe anemia can reduce the total blood volume, leading to orthostatic hypotension.

Adrenal Insufficiency: Although rare, adrenal insufficiency (e.g., Addison's disease) can cause orthostatic hypotension due to the lack of cortisol and aldosterone, which are crucial for maintaining blood pressure.
Pheochromocytoma: Paradoxically, some patients with pheochromocytoma can experience orthostatic hypotension, particularly if they have a significant drop in blood pressure when standing due to vasodilation.
Multiple System Atrophy (MSA): A neurodegenerative disorder that can cause autonomic dysfunction, leading to severe orthostatic hypotension.

Pure Autonomic Failure (PAF): A rare condition characterized by progressive autonomic dysfunction, leading to severe orthostatic hypotension.
Dopamine Beta-Hydroxylase Deficiency: A rare genetic disorder affecting the production of norepinephrine, leading to severe orthostatic hypotension.
Familial Dysautonomia (Riley-Day Syndrome): A rare genetic disorder that affects the development of the autonomic nervous system, leading to various symptoms including orthostatic hypotension.