Viagra: the side effects explained

To best understand the side effects of Viagra, it’s important to know what the drug actually does and how it works.

Viagra is one of the most popular treatments for erectile dysfunction (ED). Alongside other brand names like Revatio and Aronix, it contains the active ingredient Sildenafil citrate which belongs to a family of drugs called PDE5 inhibitors. Other fellow PDE5 inhibitors include Vardenafil (Levitra), Tadalafil (Cialis) and Avanafil (Spedra).

These medicines work by targeting a specific enzyme responsible for the erectile tissue. This helps to relax the blood vessels and smooth muscles in the penis, allowing more blood to flow into the penis. This sequence of actions helps you to achieve and maintain an erection during sexual activity.

The most common side effects of Viagra tend to be mild and go away on their own without treatment. The manufacturer estimates that these occur in around 1 in every 10 patients on Viagra.

We’re going to list some of the most common side effects and what causes them. You should still always read the patient information leaflet to familiarise yourself with all of the potential side effects.

Headaches

Headaches are the only side effect that is listed as ‘very common’ in the Viagra patient information leaflet, of which Pfizer (the manufacturer) estimates happens in more than 1 in every 10 men on Viagra.

Viagra can cause headaches because of Sildenafil’s effects on the blood vessels. It doesn’t just affect the blood vessels in the penis, but also across the body. Most notably in the lungs, as Sildenafil is used as a treatment for pulmonary arterial hypertension.

It can also affect the blood vessels surrounding the brain. As they increase in diameter, they become more prominent and tender which stretches the nerves around them. This triggers your nervous system to send a ‘pain’ message to your brain, which causes the headache.

Nasal congestion

Another side effect of Sildenafil is a stuffy nose or blocked nose and sinuses. This occurs due to the blood vessel changes that happen in the nasal passages.

One of the main chemicals present in Sildenafil’s mechanism of action is nitric oxide (NO). The chemical also resides in the tissues in the nasal cavity. That means, once you take Viagra, the blood vessels in your nose also expand. This then causes the nose to become congested.

Flushing

Flushing is a side effect of Viagra which causes widespread redness across the face. Much like headaches and nasal congestion, this is caused by blood vessels widening.

When the blood vessels in the face dilate, this causes the skin to become red. Most men notice this facial flushing in their nose, cheeks and forehead. You may also find that your skin is warm in the flushed areas.

Indigestion

Indigestion is a common term to describe acid reflux and heartburn. This condition is temporary for most, and occurs when acid from your stomach leaks into your oesophagus. But why does Viagra cause these effects?

Sildenafil relaxes the smooth muscles in this penis to allow for more blood flow. This can affect other smooth muscles in your body, one of these being a bundle of muscles known as the lower esophageal sphincter (LES).

The LES functions as a valve between your oesophagus and your stomach and its function is to keep stomach acid down. However when it relaxes, it allows some stomach acid to escape through which is what causes heartburn. Viagra relaxes these muscles, which can result in mild heartburn.

Other less common side effects

Other side effects are estimated to affect around 1 in 100 men on Viagra, and can range in severity.

Some uncommon side effects include:

• skin rash
• vomiting or nausea
• muscle pain (e.g in arm, leg or back pain)
• feeling sleepy
• vertigo
• dry mouth
• blood in urine
• nosebleeds

For a full list of common and uncommon side effects, please refer to the patient information leaflet.

More severe side effects of Viagra are rare (only affecting an estimated 1 in every 1,000 men on Viagra), but it can be scary to read them when you’re just starting a new medicine.

We’re going to list a few of the most worrisome ones, how likely they are to occur and what you should look out for if you experience any of these.

Prolonged erections

A prolonged erection, a condition known as priapism, occurs when the blood that fills the penis to make it erect gets trapped and cannot flow back out again. These tend to be painful erections that last a long time (longer than 2 hours) and don’t disappear after orgasm.

However, Viagra and other PDE5 inhibitors are very unlikely to cause priapism on their own. In fact, one study reviewed priapism cases reported to the FDA (Food and Drugs Administration) in the US and found that only 2.9% of reported cases in healthy men were linked to PDE5 inhibitor-use.

The condition mainly occurs in those who have another health condition or take another ED treatment on top of Viagra such as penile injections (e.g Alprostadil).

Visual disturbances

Another rare side effect reported with Viagra use is abnormal vision. Reported side effects include:

• blurred vision or loss of peripheral vision
• photophobia - sensitivity to bright lights
• cyanopsia - blue-tinted vision
• non-arteritic anterior ischemic optic neuropathy (NAION) - loss of vision due to lack of blood flow damaging the optic nerve

A majority of these vision problems are believed to be caused by Viagra’s effect on a specific enzyme in the retina. This enzyme is another phosphodiesterase type called PDE6, and because it’s closely related to PDE5, Viagra can sometimes have an effect on it.

According to research, these side effects are more common in those on higher doses of Viagra and are often temporary, usually lasting no longer than 5 hours.

Heart problems

Side effects related to the heart take up a fair portion of the rare side effects list. This is because Viagra affects the blood vessels across the body.

Some reported cardiovascular side effects include:

• chest pain (angina)
• irregular heartbeat (arrhythmia)
• high blood pressure
• low blood pressure
• heart attack
• heart failure
• stroke

Whilst this list may look long, there are a couple of factors you need to consider. The first is that the incidence of a cardiovascular event from taking Viagra is low, studies report an incidence as low as 3%.

Another factor to consider is that these conditions and erectile dysfunction share similar risk factors including high cholesterol, obesity, type 2 diabetes and heart disease. During Viagra’s post-marketing experience in 1998, of the 128 cardiovascular deaths related to Viagra, 70% already had some kind of cardiovascular disease. This means it’s difficult to identify a definite causal relation.

However the risk is still present, so those who have a history of heart disease are advised to take the low dose of Viagra (25mg).

Hearing loss

A few cases of sudden hearing loss have been reported in Viagra users. It is a condition known as sensorineural hearing loss, sometimes referred to as “Viagra deafness”, which is caused by damage to the structures in the inner ear or auditory nerve. It is often accompanied by tinnitus and dizziness.

Many studies have investigated this link but a causal relationship has not been clearly defined nor is it understood why Viagra causes it.

Regardless, if you experience any loss of hearing whilst using Viagra, you should seek immediate medical attention to prevent permanent hearing damage.

Seizures

One of the rarest reported side effects of Viagra are seizures. In 2002, one study reported two cases of healthy men who had suffered tonic-clonic seizures shortly after taking Viagra.

Similar complications have also been found in cases of men who have taken Vardenafil as well as several studies on mice that have found that Sildenafil has a proconvulsant effect.

It’s a rare phenomenon, and not well understood. Experts have observed multiple effects on the brain in mice that could result in seizures, but a probable cause has yet to be identified.

Because you only need to take Viagra as and when you need it, Viagra has a low risk of long-term side effects. One study monitored the safety and efficacy of Viagra across 4 years. Of which, only 3.8% people experienced non-serious side effects with only 6.3% deciding to discontinue treatment.

If you have a pre-existing medical condition or take certain medications, you may be more likely to experience side effects than other men, such as if you:

• have a blood disorder e.g sickle cell anaemia or leukaemia
• have a deformity of the penis e.g Peyronie’s disease
• have a stomach ulcer
• take any other treatments for ED
• take ritonavir for HIV

Some men are at an even higher risk of serious side effects, and should not take Viagra at all for that reason.

This includes men who have:

• had an allergic reaction to Viagra or Sildenafil in the past
• a severe heart or liver problem
• low blood pressure
• recently had a stroke or heart attack
• a rare inherited eye disease such as retinitis pigmentosa
• experienced vision loss caused by NAION

If you take any medications, including any over-the-counter or herbal supplements, you should always check with your healthcare provider before starting Viagra. This is because a few medicines can also cause a dangerous and sudden decrease in blood pressure when taken with Viagra, including:

• nitrates for chest pain
• nitric oxide donors (e.g amyl nitrate, otherwise known as “poppers”)
• riociguat for pulmonary arterial hypertension
• alpha-blockers for high blood pressure or prostate enlargement

To reduce the risk of drug interactions or severe adverse effects, always consult a healthcare professional before taking Viagra.

Why shouldn’t women take Viagra?

Viagra is not licensed for treating sexual disorders in women, mainly because the effects are not well studied or known. Whilst PDE5 also exists in the smooth muscles of female genitalia and studies suggest increasing blood flow using Sildenafil could facilitate arousal in women, the benefit is evidently lower with the same risk of side effects as it is in men. Meaning, the cost is not much greater than the reward. Data is also incredibly limited with mixed results. It therefore goes without saying that Viagra is also not suitable for pregnant or breastfeeding women.

Most common Viagra side effects should go away on their own. However if they are bothersome, you can get over-the-counter treatments from a pharmacy such as for heartburn, muscle pain or headache.

If you experience any severe or worrisome side effects, you should stop taking Viagra and consult your doctor. They may recommend you take a lower dose of Viagra or switch to an alternative.

Here at euroClinix, we offer a discreet, online erectile dysfunction service. We offer all 3 doses of Viagra, so you can get the dosage that works best for you. On top of that, the consultation is free! Our UK registered doctors will review your consultation and prescribe the medicine online.