Can hypothyroidism cause hypotension?

Hypothyroidism and Blood Pressure: The Hypertension Connection

Hypothyroidism typically causes hypertension (high blood pressure), not hypotension (low blood pressure), particularly diastolic hypertension due to increased systemic vascular resistance.

Cardiovascular Hemodynamics in Hypothyroidism

Hypothyroidism causes a characteristic pattern of increased vascular resistance and elevated blood pressure, not low blood pressure. The key hemodynamic changes include:

• Systemic vascular resistance increases by up to 50% in hypothyroid patients 1
• Diastolic hypertension is the predominant blood pressure abnormality, resulting from markedly elevated peripheral resistance 1, 2
• Bradycardia (slow heart rate) is one of the most common cardiovascular manifestations 1
• Low cardiac output results from the combination of bradycardia, decreased ventricular filling, and decreased cardiac contractility 1

Clinical Evidence for Hypertension in Hypothyroidism

The relationship between hypothyroidism and elevated blood pressure is well-established:

• Hypothyroidism was found in 3.6% of 688 consecutive hypertensive patients, and thyroid hormone replacement normalized blood pressure (below 90 mm Hg diastolic) in 32% of these patients 3
• Induction of hypothyroidism by radioiodine therapy significantly increased diastolic blood pressure above 90 mm Hg in 40% of patients, which was reversible with thyroid hormone replacement 3
• Daytime diastolic blood pressure significantly increased during the hypothyroid state (84.6 vs. 76.4 mm Hg) in normotensive patients who stopped thyroid hormone replacement 4

Mechanisms of Blood Pressure Elevation

The hypertension in hypothyroidism is driven by multiple mechanisms:

• Increased aortic stiffness is a key factor—patients with hypertension and hypothyroidism show significantly elevated aortic stiffness index compared to controls 2
• Sympathetic and adrenal activation occurs, with noradrenaline levels nearly doubling (2954 vs. 1574 pmol/L) and aldosterone doubling (310.3 vs. 156.9 pmol/L) during hypothyroidism 4
• Volume-dependent mechanisms with low plasma renin activity contribute to blood pressure elevation 5

Clinical Implications and Pitfalls

Important caveats to recognize:

• Despite significant hemodynamic changes, clinical heart failure is relatively rare in hypothyroidism because cardiac output is usually sufficient to meet the lowered systemic metabolic demands 1
• Severe, untreated hypothyroidism progressing to myxedema coma can present with hypotension, hypothermia, and altered mental status—this is a life-threatening emergency with up to 30% mortality 6
• Only 50% of hypertensive hypothyroid patients achieve complete blood pressure normalization with thyroid hormone replacement alone; the remainder may require additional antihypertensive therapy due to persistent aortic stiffness 2

Treatment Approach

Thyroid hormone replacement is the primary intervention:

• Levothyroxine therapy decreases blood pressure in most hypothyroid patients with hypertension 2, 3
• For patients with persistent hypertension after achieving euthyroidism, calcium channel blockers (such as felodipine) can further reduce blood pressure and aortic stiffness 2
• TSH monitoring should occur 6-8 weeks after initiating or changing levothyroxine dose, then annually once at goal 6

The bottom line: If you encounter a patient with hypothyroidism and low blood pressure, look for alternative causes of hypotension or consider myxedema coma if severely hypothyroid with other concerning features.