ED medicine side effects and safety

What are the common side effects of ED medicines?

Headache, facial flushing, indigestion, a blocked or runny nose and dizziness are the most common side effects of both sildenafil and tadalafil. They come from the same blood-vessel widening that helps the erection, and usually pass as the medicine wears off.

In the trials summarised in the US FDA label for sildenafil, headache affected about 16 in 100 men and flushing about 10 in 100, compared with far fewer on placebo. Each medicine has a slightly different pattern:

Side effect	Sildenafil (Viagra)	Tadalafil (Cialis)
Headache	very common	very common
Flushing	common	less common
Indigestion or reflux	common	common
Blocked or runny nose	common	common
Blue-tinged or blurred vision, light sensitivity	occasional	uncommon
Back pain, muscle aches	occasional	common, often 12 to 24 hours later
Dizziness	occasional	occasional
How long side effects last	a few hours	up to a day or two

Simple measures help with mild effects: drinking enough water (dehydration in the Philippine heat worsens headaches), standing up slowly, and avoiding heavy drinking. If a side effect bothers you, tell your doctor. A different strength, or switching between sildenafil and tadalafil, often solves it. Never adjust the amount on your own.

What are the serious side effects?

Serious side effects are rare: priapism, sudden vision loss, sudden hearing loss, heart symptoms and severe allergic reactions. Each needs urgent medical care, not a wait-and-see approach.

Priapism: an erection lasting more than 4 hours

Priapism is an erection that will not go down, often painful, lasting 4 hours or more. Blood trapped in the penis stops carrying oxygen, and the tissue can be permanently damaged within hours. The NHS advises going to an emergency department straight away.

It is rare with PDE5 inhibitors but more likely in men with sickle cell disease, leukaemia or multiple myeloma, a penis deformity, or when ED medicines are combined with other ED treatments such as injections. In the Philippines, go to the nearest hospital emergency room; do not wait for a clinic appointment the next day.

Sudden vision loss and NAION

Sudden loss of vision in one or both eyes needs urgent care. A rare condition called NAION (non-arteritic anterior ischaemic optic neuropathy), in which blood flow to the optic nerve is reduced, has been reported in men taking PDE5 inhibitors.

It has not been proven that the medicines cause NAION, because many of the men affected already had risk factors such as diabetes, high blood pressure, heart disease, smoking, age over 50, or a "crowded" optic disc. The US labels still tell men to stop the medicine and get medical help at once if vision suddenly drops. If you have ever lost vision in one eye from NAION, your doctor will usually advise against these medicines.

The temporary blue tinge or light sensitivity some men notice with sildenafil is different. It comes from a mild effect on an enzyme in the retina and fades within hours.

Sudden hearing loss

Sudden decrease or loss of hearing, sometimes with ringing in the ears or dizziness, has been reported rarely after PDE5 inhibitors. Stop the medicine and get medical care promptly. As with NAION, a direct cause has not been established.

Chest pain, fainting or palpitations

Sex is physical exertion, and ED often travels with heart disease. If you have chest pain, faint or feel your heart racing irregularly during or after sex, stop, rest, and call for help. Tell responders which ED medicine you took and when, because it changes what they can safely give you (see nitrates below).

Severe allergic reactions

Swelling of the face, lips, tongue or throat, trouble breathing or a severe rash are signs of a serious allergic reaction. Call for emergency help.

Who should not take ED medicines?

Men on nitrates or riociguat must never take PDE5 inhibitors. Men with a recent heart attack or stroke, unstable heart disease, very low blood pressure, severe liver disease or certain eye conditions need a doctor's careful assessment first.

The full lists are on the sildenafil and tadalafil pages. A doctor's check usually covers your blood pressure, heart symptoms (can you climb two flights of stairs without chest pain?), medicines, alcohol use and eyes. That check is the main reason these medicines are prescription-only in the Philippines.

Which medicines interact with ED medicines?

The dangerous interactions are nitrates and riociguat. Alpha blockers, other blood pressure medicines, strong CYP3A4 inhibitors and grapefruit also change how ED medicines behave.

Nitrates: the one rule never to break

Nitrates treat angina and include glyceryl trinitrate (nitroglycerin) tablets or spray under the tongue, isosorbide mononitrate and dinitrate tablets, and nitrate patches. Recreational "poppers" (amyl nitrite) are nitrates too. Combined with sildenafil or tadalafil they can drop blood pressure to dangerous levels.

If you carry a nitrate for chest pain, even one you rarely use, do not take an ED medicine. If you take an ED medicine and then develop chest pain, tell emergency staff. For tadalafil, the US label says at least 48 hours should pass after the last dose before a nitrate is given, and only under medical supervision.

Riociguat

Riociguat treats some forms of pulmonary hypertension. It acts on the same pathway, and the combination is contraindicated.

Blood pressure and prostate medicines

High blood pressure is common in Filipino men, and many take amlodipine, losartan or similar medicines. These usually can be combined with ED medicines under a doctor's guidance, though each adds a small extra drop in pressure.

Alpha blockers such as tamsulosin, doxazosin and terazosin, used for prostate symptoms and sometimes blood pressure, need more care: together with a PDE5 inhibitor they can cause dizziness or fainting on standing. Your doctor may change timing or strength, or choose another option.

CYP3A4 inhibitors and inducers

Some medicines slow the liver's breakdown of sildenafil and tadalafil and raise their levels: ritonavir and other HIV protease inhibitors, ketoconazole and itraconazole, and clarithromycin and erythromycin. Others, such as rifampicin (widely used for tuberculosis in the Philippines), speed up the breakdown and can make ED medicines less effective. Tell your doctor about any of these.

Grapefruit

Grapefruit and grapefruit juice can raise sildenafil and tadalafil levels. Pomelo, a close relative and common here, may have a similar effect. Ask your pharmacist.

Other ED treatments

Never combine two PDE5 inhibitors, and never combine them with injections or other ED treatments unless a specialist directs it. "Herbal" products often hide a PDE5 inhibitor, which can mean an unintended double dose.

Can you drink alcohol with ED medicines?

A small amount is unlikely to be dangerous for most men, but heavy drinking adds to dizziness and low blood pressure and makes erections harder to get. With tadalafil, the US label found that 5 or more units of alcohol increased dizziness and blood pressure drops on standing.

The practical advice: if you drink, keep it light. Many men who say their medicine "did not work" had been drinking heavily. If alcohol is a regular part of your week, tell your doctor honestly.

Are fake ED pills a safety risk?

Yes, and in the Philippines they are probably the biggest one. Counterfeit and unregistered tablets, and "herbal" sex enhancers, can contain the wrong amount of drug, a different drug, or contaminants.

The US FDA has warned about hundreds of sexual enhancement products sold as natural that were found to contain hidden sildenafil, tadalafil or similar drugs, sometimes at high doses or in combination. A man on nitrates who takes one of these may not know he is taking a PDE5 inhibitor at all. Pills from marketplaces, social media sellers and unregistered imports carry this risk.

The safe route is simple: a prescription from a licensed doctor, filled at a licensed pharmacy such as Watsons, Mercury Drug, Southstar Drug, Rose Pharmacy or TGP, with the product checked on the FDA Philippines verification portal. Registered generics such as Zilden and Spiagra are inexpensive, so there is little reason to take the risk; see sildenafil prices. Our guide on how to spot fake ED pills shows what to look for.

When should you seek urgent care?

Go to an emergency room for an erection lasting more than 4 hours, sudden loss of vision or hearing, chest pain, fainting, or signs of a severe allergic reaction. Tell the staff which ED medicine you took and when.

For milder side effects that persist or worry you, contact your doctor or the prescribing telehealth service. They can adjust your treatment safely. If you have not yet had a proper check, a consultation is the place to start: it confirms the medicine suits your heart and your other medicines, and it looks for causes of ED worth treating in their own right. Read more about online ED consultation or return to the ED medicines overview.

Frequently asked questions

What are the most common side effects of Viagra?+

Headache and facial flushing are the most common, followed by indigestion, a blocked nose, dizziness and a temporary blue tinge to vision. They usually fade within a few hours as the medicine wears off.

How long do sildenafil side effects last?+

Most last a few hours, in line with sildenafil's roughly 4-hour action. Tadalafil side effects, such as back pain, can last a day or two because tadalafil stays in the body longer.

Can ED medicine cause a heart attack?+

In men whose doctor has checked their heart, PDE5 inhibitors have not been shown to raise heart attack risk. The danger comes from combining them with nitrates or using them with unstable heart disease, which is why a doctor's check matters.

What should I do if an erection lasts more than 4 hours?+

Go to the nearest emergency room. Priapism can permanently damage the penis if not treated within hours, and it is not something to wait out.

Is it safe to take Viagra with blood pressure medicine?+

Often yes, under a doctor's guidance, but never with nitrates. Alpha blockers and other blood pressure medicines can add to dizziness, so your doctor needs your full medicine list.