The nitrate rule
Nitrates also raise cGMP. Combined with a PDE5 inhibitor, the effect stacks and blood pressure can fall suddenly and dangerously. All four labels list nitrates as a contraindication, meaning never combine them.
- Prescription nitrates: nitroglycerin (tablets, spray, patches, ointment), isosorbide mononitrate, and isosorbide dinitrate, usually prescribed for angina.
- "Poppers": amyl, butyl, or other alkyl nitrites sold as recreational inhalants. They carry the same risk.
In an emergency, doctors need to know when you last took a PDE5 inhibitor. The labels say nitrates shouldn't be given until at least 24 hours after sildenafil, 48 hours after tadalafil, and 12 hours after avanafil, and only with close medical monitoring.
Other interactions
| Medication or substance | What to know |
|---|---|
| Riociguat (Adempas) | Contraindicated. Used for pulmonary hypertension; the blood pressure effect stacks the same way nitrates do. |
| Vericiguat (Verquvo) | A heart failure drug that works on the same pathway. Combining is not recommended. |
| Alpha-blockers (tamsulosin, alfuzosin, doxazosin, terazosin, and others) | Often prescribed for prostate symptoms. Both lower blood pressure, so dizziness or fainting can happen. Prescribers usually want you stable on the alpha-blocker first and start the PDE5 inhibitor at a low dose. |
| Other blood pressure drugs | Usually fine, but the combined effect can cause lightheadedness. Tell your prescriber everything you take. |
| Strong CYP3A4 inhibitors (ritonavir and other HIV medications, ketoconazole, itraconazole, clarithromycin) | Can sharply raise PDE5 inhibitor levels. Lower doses or longer intervals are needed, and some combinations are avoided entirely. |
| Alcohol | Several drinks add to the blood pressure drop and work against erections on their own. |
| Grapefruit juice | Can raise levels of some PDE5 inhibitors. Large amounts are best avoided. |
| Another PDE5 inhibitor | Don't combine them, including "stacked" compounded products. That includes Revatio or Adcirca, which are the same drugs prescribed for pulmonary hypertension. |
Common side effects
Most side effects are mild, come from the same blood-vessel relaxation that helps erections, and fade within hours.
- Headache, the most common.
- Facial flushing or warmth.
- Stuffy or runny nose.
- Indigestion or heartburn.
- Back pain and muscle aches, mostly with tadalafil.
- Vision changes like a blue tint, blurriness, or light sensitivity, mostly with sildenafil and vardenafil.
- Dizziness, especially when standing up quickly or combined with alcohol or blood pressure drugs.
If side effects bother you, a lower dose or a different drug often helps. Talk to your prescriber rather than splitting or stacking pills on your own.
Rare emergencies
These are uncommon, but the labels warn about them because speed matters:
- An erection lasting more than 4 hours (priapism). Go to an emergency room. Without prompt treatment it can permanently damage the penis.
- Sudden loss of vision in one or both eyes. A rare optic nerve problem (NAION) has been reported in men taking PDE5 inhibitors. Stop the drug and get emergency care.
- Sudden hearing loss or ringing, sometimes with dizziness. Stop the drug and get prompt medical care.
- Chest pain, fainting, or severe dizziness during or after sex. Call 911.
Talk to a doctor first if...
These conditions don't always rule out treatment, but they need an individual decision from a clinician who knows your history:
- A heart attack, stroke, or serious heart rhythm problem in the last 6 months.
- Chest pain (angina), especially if it's unstable or comes on during sex.
- Heart failure, or a narrowed heart valve such as aortic stenosis.
- Very low or uncontrolled high blood pressure. Blood pressure guide →
- Severe liver disease, or kidney disease requiring dialysis.
- Retinitis pigmentosa or a past optic nerve problem (NAION).
- Conditions that raise priapism risk, like sickle cell anemia, multiple myeloma, or leukemia, or a curved or scarred penis (Peyronie's disease).
- A bleeding disorder or an active stomach ulcer.
Be honest on any intake form, including about poppers and other recreational drugs. Prescribers can't protect you from interactions they don't know about.
Is sex safe for my heart?
Sex is roughly as physically demanding as climbing two flights of stairs briskly. The American Heart Association's guidance is that men with stable heart disease who can manage that level of activity without symptoms can generally have sex safely. If you can't, or you have new symptoms, get evaluated first.
And if ED is new, it's worth asking whether your heart is part of the reason. Heart & metabolic health →