Tadalafil is a phosphodiesterase 5 inhibitor. That means it decreases the activity of phosphodiesterase 5, an enzyme that breaks down a substance called cyclic guanosine monophosphate. The lungs and other parts of the body produce cGMP, which causes arteries to relax and widen.

When tadalafil decreases the enzyme’s activity, more cGMP is available to relax or widen the blood vessels inside the lungs. When the blood vessels relax and widen, it’s easier for the heart to pump blood through the lungs, which reduces blood pressure in the lungs. That usually leads to improved exercise ability and wellbeing.

The recommended dose for most patients is 40 mg (two 20 mg tablets) once daily, with or without food.

• Don’t split, crush or chew tablets.
• Your physician might start you on one tablet a day then move you to the full dose of two tablets daily. The gradual change will allow you to adjust to the medication.

A physician must prescribe tadalafil, and your insurance company must approve coverage before you start therapy. Depending on your insurance, you might fill your prescription at a retail pharmacy or through a specialty pharmacy such as Accredo, Aetna, Alliance Rx Walgreens Prime, Axium, BriovaRx, Cigna, CVS specialty, Humana and Kaiser Permanente.

Tadalafil is generally well tolerated. You don’t need regular bloodwork for side effects. Your health care team might ask you to regularly monitor your blood pressure, especially in your first few days of treatment or when your dose increases. Most patients don’t need blood pressure monitoring.

Potential side effects include:

• Muscle pain
• Nasal stuffiness
• Respiratory infection
• Leg or arm pain
• Back pain
• Upset stomach

No differences in side effects have been reported among men and women with PAH. Studies haven’t shown an effect on sexual function in women who take tadalafil.

Allergic reaction
Allergies to this medication are possible but unlikely. Any medication can cause side effects or sensitivities. Check with your doctor if you experience a rash or throat tightening.

Low blood pressure
Tadalafil relaxes blood vessels throughout the body, which can lower systemic blood pressure. People with low blood pressure (lower than 90/50 ) should use tadalafil with caution.

Prolonged erection
Prolonged erection (greater than four hours) is rare but very serious. If you have a prolonged erection, go to an emergency room or contact your doctor immediately.

Vision loss
Sudden vision loss in one or both eyes has occurred with PDE5 inhibitors. Sudden vision loss could indicate serious dysfunction of the optic nerve and requires immediate medical attention.

Rare cases of blindness have been reported with PDE5 inhibitors, including forms of tadalafil, but not Adcirca. This type of blindness, non-arteritic anterior ischemic optic neuropathy, can be permanent. It’s not yet known whether the blindness is related to tadalafil or to underlying cardiovascular diseases that place people at risk for this particular type of blindness, even without tadalafil use.

Hearing loss
Sudden hearing loss is possible and could be accompanied by dizziness and/or ear ringing. Seek prompt medical attention if those side effects occur.

If you experience any of these side effects, seek immediate medical attention.

Certain patient populations must take precautions while taking tadalafil, while others should avoid it. Learn about who can and who shouldn’t take this medication:

Pregnant and breastfeeding patients
Tadalafil hasn’t caused harm to animal fetuses in research studies. However, there hasn’t been adequate research on birth defects in humans. In clinical practice, tadalafil is commonly used in pregnant and lactating women with severe pulmonary arterial hypertension, as the risk of untreated or undertreated PAH is higher than the risk of adverse effects from tadalafil.

Children and teens
Tadalafil generally seems safe and effective for pediatric patients. Although clinical trials for pediatric PAH patients have been small and included people with a wide range of ages and diseases, the sixth World Symposium on Pulmonary Hypertension in 2019 recommended PDE5 inhibitors in its pediatric PAH treatment algorithm.

People with liver disease
There is limited research on tadalafil for people with liver disease. For those with mild or moderate liver disease (Child Pugh Class A or B), doctors should consider starting tadalafil at 20 mg once daily. People with severe liver disease (Child Pugh Class C) should avoid tadalafil.

People with kidney disease
People with mild to moderate kidney disease (creatinine clearance 31 to 80 ml/min) should start tadalafil at 20 mg once daily and increase to 40 mg once daily based on how well they tolerate the medication and side effects.

People with severe kidney disease (creatinine clearance greater than 30 ml or on dialysis), generally should avoid tadalafil. Severe kidney disease increases the amount of tadalafil in the bloodstream, even when patients are on dialysis.

People with HIV/AIDS
If you have human immunodeficiency virus (HIV or AIDS), consult your pharmacist before taking phosphodiesterase inhibitors such as tadalafil, which can impair the efficacy of some antiretrovirals.

Other conditions
Tadalafil isn’t recommended for people with two rare diseases often associated with PAH: pulmonary veno-occlusive disease and pulmonary capillary hemangiomatosis.

Use tadalafil with caution if you have dehydration, left heart diseases and abnormalities of the nervous system.

People with retinitis pigmentosa shouldn’t take tadalafil, although there is no research to determine whether the medication is beneficial or safe for those patients.

Don’t take nitrates in any form while taking tadalafil because the combination can cause systemic blood pressure to fall to unsafe levels. That includes nitric oxide donors or alpha blockers, which generally are used to treat high blood pressure.

Use caution taking tadalafil with other medications that lower blood pressure, as well as alcohol. Tadalafil is broken down predominantly by an enzyme called CYP3A in the liver. It can cause significant interactions with medications that target this enzyme pathway.

Simultaneous use of bosentan and tadalafil can decrease tadalafil levels in blood. However, it’s usually not necessary to change the doses of these two medications together.