Tadalafil (brand name Cialis) is primarily prescribed to manage erectile dysfunction (ED) and the symptoms of benign prostatic hyperplasia (BPH). The drug functions as a potent vasodilator, causing blood vessels to widen throughout the body. Because its mechanism of action is tied to the relaxation of vascular tissue, Tadalafil definitively lowers blood pressure. This effect is an intrinsic property of the compound, and while often mild, it is the fundamental reason the drug works for its intended purposes.
How Tadalafil Causes Blood Vessel Relaxation
Tadalafil is classified as a phosphodiesterase type 5 (PDE5) inhibitor. This means it targets the PDE5 enzyme, which breaks down cyclic Guanosine Monophosphate (cGMP). cGMP is a powerful signaling agent that tells the smooth muscle cells lining blood vessel walls to relax, a process known as vasodilation.
By inhibiting PDE5, Tadalafil prevents the rapid breakdown of cGMP, causing its concentration to increase. This accumulation signals a sustained state of relaxation in the blood vessel walls, leading to their widening. The resulting increase in blood vessel diameter allows blood to flow more easily, which causes the drop in systemic blood pressure. This vasodilation occurs wherever PDE5 is present, including in the pulmonary arteries and throughout the systemic circulation.
The Extent of Blood Pressure Changes
The blood pressure-lowering effect of Tadalafil is generally mild and temporary in healthy individuals without pre-existing cardiovascular conditions. Clinical studies show that a typical dose may reduce systolic blood pressure by approximately 2 to 4 mmHg and diastolic pressure by a similar small margin. This slight reduction is often clinically insignificant for most users and does not typically cause noticeable symptoms.
For patients with high blood pressure who are taking other antihypertensive medications, the reduction can be more pronounced. Tadalafil has been shown to reduce mean ambulatory blood pressure by up to 7.5 mmHg systolic and 4.3 mmHg diastolic in some hypertensive individuals. Despite this additive effect, Tadalafil is considered safe to use with most common blood pressure medications, though close monitoring is advisable.
Tadalafil for Pulmonary Arterial Hypertension (PAH)
The vasodilating action of Tadalafil is the desired therapeutic effect in treating Pulmonary Arterial Hypertension (PAH). PAH is a serious condition characterized by high blood pressure specifically in the arteries of the lungs. Tadalafil is prescribed to relax the pulmonary blood vessel walls, lowering the pressure in the lungs and reducing the strain on the right side of the heart.
Dangerous Drug Combinations
Combining Tadalafil with certain other medications poses a significant risk of a life-threatening drop in blood pressure, known as profound hypotension. The most critical interaction is with any form of Nitrate medication, such as nitroglycerin, isosorbide dinitrate, or isosorbide mononitrate, used to treat chest pain or angina. Nitrates increase the production of cGMP, while Tadalafil prevents cGMP from being broken down.
Combining these drugs results in a synergistic buildup of cGMP, causing excessive and uncontrolled relaxation of smooth muscle. This massive vasodilation can cause a precipitous fall in blood pressure that restricts blood flow to the heart and brain. Therefore, the use of Nitrates is an absolute contraindication for Tadalafil. Patients must wait a minimum of 48 hours after taking Tadalafil before taking any Nitrate medication.
The risk of severe hypotension also increases when Tadalafil is taken alongside certain Alpha-Blockers. Alpha-blockers, such as doxazosin or tamsulosin, are used to treat high blood pressure and benign prostatic hyperplasia, and they also cause vasodilation. Healthcare providers typically recommend starting Tadalafil at the lowest possible dose only after a patient has been stabilized on their Alpha-Blocker regimen to minimize the risk of a dangerous interaction.