Medications that Interact with Viagra and Cialis

Viagra and Cialis are prescription meds that are used to treat erectile dysfunction (ED or impotence) in males. These PDE5 inhibitors primarily affect the genital area but they also slightly dilate the vessels throughout the body. This factor is associated with possible interactions of these anti-ED tablets with a number of other medications.

Nitrates

NEVER take nitrates in combination with Viagra or Cialis. This can be very dangerous for your health. Nitrates are powerful medicines that lead to a pronounced decrease in blood pressure in humans. Examples of these medicines include nitroglycerin and isosorbide dinitrate. The use of PDE5i medicaments can potentiate the powerful hypotensive effect of nitrates, which may lead to an unsafe reduction in arterial pressure. Symptoms may be minor, for example dizziness, but in some cases a stroke, a heart attack and even a fatal outcome are possible.

Alpha-Blockers for Hypertension

Viagra and Cialis should be used with caution in combination with alpha-blockers. This is due to the fact that both PDE5 inhibitors and α–blockers have a vasodilating effect and lead to a reduction in blood pressure. Cialis and Viagra themselves have no pronounced antihypertensive effect. But in combination with alpha-blockers, the additive effect can be observed. In some men, this combination significantly reduces the pressure and they begin to experience symptoms of hypotension, such as dizziness and fainting.

Some considerations (according to Drugs.com):

• In case of hemodynamic instability with the use of alpha-blockers, the risk of sudden hypotension due to combining tadalafil (or sildenafil) and blocker is quite high. Stability is a necessary condition for the initiation of safe therapy with PDE5 inhibitors.

• If a man is stable when using alpha-blockers, which are medicines for the treatment of hypertension, the administration of PDE5 inhibitors should begin with the lowest recommended dose.

• If a man already takes anti-ED tablets in an adjusted and optimized dosage, administration of alpha-blockers should begin with a minimum dosage. Increasing the dosage should be done slowly, this may be due to the onset of symptoms of hypotension.

• The risk of unwanted pressure reduction with the combined use of Viagra/Cialis and alpha-blockers is increased by other factors, such as the administration of other antihypertensive meds.

Other Antihypertensive Medications

Other medications for the treatment of hypertension can also interact negatively with PDE5i meds.

For example, according to some studies, the joint administration of sildenafil in 100mg dosage and amlodipine (10 or 5mg) leads to a decrease in systolic pressure by 8 points while diastolic pressure decreases by 7 points. Amlodipine belongs to the calcium channel blocker class.

Guanylate Cyclase Stimulators

This group of medicines is used to treat pulmonary arterial hypertension (PAH) and its complicated cases. It leads to an increase in NO levels in the body. A well-known representative of this group is the medicament Riociguat (trade name Adempas). It is not recommended to use Viagra if you are undergoing therapy with Adempas (official site). The same goes for Cialis.

Potent CYP3A4 Inhibitors

CYP3A4 inhibitors are medicines that inhibit the work of CYP3A4 enzyme, which is predominantly found in the intestine & liver. Its goal is to oxidize small foreign substances (agents), like toxins & medications, so that they may be removed from the human organism. The CYP3A4 inhibitors group includes some antifungal medicines, anti HIV drugs and antibiotics. Studies show that some CYP3A4 inhibitors can increase the level of anti-ED agent in the blood plasma by about three fold.

If patients use medications from this group, for example, ritonavir, ketoconazole, saquinavir, and erythromycin, the dose of PDE5 inhibitors should be reduced. The maximum recommended dosage of Cialis is 10 mg when using on demand. In this case, the Cialis tablet should be administered no more than once in 72 hours (3 days). When used on a daily basis, the maximum recommended dose of tadalafil is 2.5 milligrams per day. You must read "Cialis dosage options" topic.

As for Viagra, the maximum allowable initial dosage of it should be 25 mg. Increasing the dosage is possible only with the permission of the doctor.

It should be noted that there are antibiotics that do not belong to the powerful CYP3A4 inhibitors and do not interact with Viagra or Cialis. If you periodically use PDE5 inhibitors, keep this in mind when receiving antibiotic treatment.

Other Medications for the Treatment of Erectile Dysfunction

The safety of using Viagra and Cialis simultaneously with other medications to treat erectile problems has not been investigated. Doctors usually advise not to combine PDE5i drugs with other anti-ED meds to avoid an undesirable reduction in arterial pressure. Also, you shouldn’t combine different PDE5 inhibitors with each other, for example, Viagra and Cialis or Levitra and Stendra*. 

*Stendra compared to Sildenafil Citrate by link.

The Bottom Line on Meds that Interact with Viagra & Cialis

Thus, several medicines can enter into dangerous or unfavorable interactions with Viagra, Cialis, and other PDE5 inhibitors. If you take any medication, especially any of those listed above, you need to tell the doctor about it and carefully read the instructions to your anti-ED medication.