Sildenafil (Viagra) Side Effects Explained
Viagra
Sildenafil is a medication used to treat erectile dysfunction (ED) that may be better known under the brand name Viagra. It can also be used to treat high blood pressure in the lungs (pulmonary arterial hypertension) at a lower dose, but we’ll focus on its use as an ED drug.
Viagra was the first erectile dysfunction medication on the market. It’s still available but can now also be bought as the generic drug sildenafil (often at a cheaper price).
In this guide, we’ll discuss the common erectile dysfunction medication sildenafil, also known as Viagra, including its side effect profile and clinical safety profile. However, rest assured that this medication is generally well tolerated and effective in overcoming ED related symptoms.
What are the most common sildenafil side effects?
Although sildenafil is taken by many men for ED without any issues, it is possible to experience side effects.
The most common sildenafil side effect is a headache which happens to more than 1 in 10 men taking the medication.
Other common side effects that impact between 1 in 10 and 100 men taking sildenafil include:
Dizziness
Changes in vision, including blurriness and colour distortion
Hot flushes
Blocked nose
Feeling sick
Indigestion
Uncommon sildenafil side effects that can affect 1 in 100 to 1000 men include:
Nose or sinus inflammation, nosebleeds
Allergic reactions
Reduced sensation
Sleepiness or fatigue
Eye pain, light sensitivity, visual changes, or inflammation4
Vertigo (feels as if the room is spinning)
Tinnitus (ringing in the ears)
High or low blood pressure
Acid reflux
Dry mouth
Stomach pain
Vomiting
Rashes
Muscle pain, pain in arms or legs
Blood in the urine
Chest pain
Feeling hot
Increased heart rate
Do Viagra and Viagra Connect share the same side effects?
Sildenafil (generic) and Viagra (brand) both contain the same active ingredient, sildenafil, and work in the same way.
The medication was first sold under the brand name Viagra by the pharmaceutical company who created the drug. Once the patent, limiting who could make the drug, ran out other pharmaceutical companies were then able to create their own version.
It’s now possible to buy either branded Viagra, Viagra Connect and generic sildenafil. All of these medications contain the same active ingredient.
Viagra Connect is a variation of Viagra that's available without a prescription. In fact, it's the first ED treatment available over the counter.
Designed to be more accessible for men seeking ED treatment, Viagra Connect is available directly from a pharmacist after a brief consultation and is limited to the 50mg version.
Therefore, the side effect profile for all of the versions of sildenafil are exactly the same.
There are other ED treatments available, which contain different active ingredients that clinically promote an erection. These can be viewed here.
Why does sildenafil cause side effects?
Sildenafil/Viagra contains the active ingredient sildenafil citrate, which belongs to the phosphodiesterase inhibitor type 5 (PDE5) family of medications.
It works by relaxing the smooth muscle in the penis, increasing blood flow and making it easier to get an erection.
By blocking PDE5, which helps relax muscle tissue and increase blood flow to the penis, it affects the body in general through a vasodilating effect. Thus, this can possibly lead to reduced blood pressure, headaches, dizziness, blocked nose, digestion issues or blurry vision.
How long do sildenafil side effects last
Sildenafil/Viagra has a relatively short-acting effect and typically lasts about 4 hours,
Sildenafil should be taken an hour before sexual activity as it doesn’t work instantly. Levels of the drug peak in the blood between 30-120 minutes after taking sildenafil tablets.
In clinical trials, men who took sildenafil on an empty stomach were able to achieve an erection in between 12 and 70 minutes. Around 82% of men experienced an erection in 45 minutes or less.
How long it takes for sildenafil to work varies from person to person, but eating before taking the medication usually means it takes longer.
Sildenafil continues to work for several hours after you take it. Based on data from clinical trials, sildenafil can still help men achieve an erection 4-5 hours after administration.
In older men and those with reduced kidney or liver function, the medication may continue to work for even longer. This is because the body is less effective at removing the drug in these situations, so levels remain higher for longer.
Do sildenafil side effects depend on dose?
The side effects are not common, the higher the dose, then the higher the likelihood of side effects to occur.
Sildenafil comes in the following strengths: 25mg, 50mg and 100mg. The starting dose is usually the 50mg version, which is the same as Viagra connect.
Can sildenafil or Viagra affect blood pressure?
As noted above - Sildenafil causes blood vessels to dilate, which causes peripheral vascular resistance to decrease. This typically leads to a modest reduction in blood pressure. In most healthy individuals taking sildenafil for erectile dysfunction at standard doses (25–100 mg), this effect is generally mild and clinically insignificant.
According to the UK Summary of Product Characteristics (SmPC), sildenafil commonly produces a small decrease in both systolic and diastolic blood pressure, usually in the range of 8–10 mmHg systolic and 5–6 mmHg diastolic pressure reduction.These changes occur approximately one hour after administration, coinciding with peak plasma concentrations of the medication.
The vasodilatory effect of sildenafil is not limited to the corpus cavernosum (the erectile tissue of the penis) but affects blood vessels throughout the systemic circulation. This is why sildenafil should not be used in patients with hypotension (blood pressure <90/50 mmHg) and in those for whom sexual activity is inadvisable due to underlying cardiovascular conditions.The blood pressure-lowering effect is generally transient, lasting several hours as the drug is metabolised and eliminated from the body.
For individuals with normal baseline blood pressure and no contraindicated medications, this modest hypotensive effect rarely causes problematic symptoms. However, alcohol consumption can increase the likelihood of postural hypotension and dizziness.
Understanding this mechanism is essential for safe prescribing and patient counselling, particularly in those with pre-existing cardiovascular conditions or those taking multiple antihypertensive medications.
Sildenafil and nitrates
Sildenafil is contraindicated in patients taking any form of nitrates or nitric oxide donors, including glyceryl trinitrate (GTN), isosorbide mononitrate, isosorbide dinitrate, and recreational 'poppers' (amyl nitrite).
When sildenafil is combined with these medications, the result can be severe, potentially life-threatening hypotension. Both drug classes work through pathways involving nitric oxide and cGMP, and their combined effect produces profound vasodilation that can cause blood pressure to drop precipitously.
Thus, patients taking nitrates should not use sildenafil under any circumstances.
Additional blood pressure related risks
Medications such as doxazosin, tamsulosin, and alfuzosin (Alpha-blockers) can cause additive hypotensive effects when combined with sildenafil. According to the BNF & NICE , patients should be stable on alpha-blocker therapy before starting sildenafil, which should be initiated at the lowest dose (25 mg).Consider separating doses with a 4 hours gap to minimise the risk of postural hypotension.
Patients taking multiple blood pressure medications may experience enhanced hypotensive effects, though these are generally modest. Careful monitoring is advisable when initiating sildenafil in these individuals.
Some patients may experience dizziness, light-headedness, or syncope (fainting) when standing up quickly (postural hypotension) after taking sildenafil, particularly if they are dehydrated, have consumed alcohol, or are taking other vasodilating medications.
Sildenafil is contraindicated in patients with severe cardiovascular conditions, including those who have had a myocardial infarction or stroke within the last 6 months, unstable angina, severe heart failure, severe left ventricular outflow obstruction (e.g., aortic stenosis), or severe hepatic impairment. The Medicines and Healthcare products Regulatory Agency (MHRA) advises caution in these populations, and sexual activity itself may pose cardiovascular risk in such patients.
Are there any long-term sildenafil side effects?
Sildenafil/Viagra is a well studied medication that is generally well tolerated with effective licensed clinical outcomes for ED.
The likelihood of long-term side effects is limited, beyond the patients in the scenarios discussed in this article.
How can you reduce sildenafil side effects?
Sildenafil works best on an empty stomach, so it’s best to avoid taking it after a large meal. You should also avoid drinking grapefruit juice while taking sildenafil as it can raise levels of the drug in the blood, meaning you’re more likely to experience side effects and negative impacts of the medication.
Drinking alcohol while taking certain erectile dysfunction medications, like avanafil, can increase the risk of low blood pressure. Studies have shown that 50mg sildenafil did not make the blood pressure-lowering effects of alcohol worse. However, there may still be a risk of low blood pressure when combining the two, so it’s best to avoid drinking large amounts of alcohol while taking sildenafil.
What serious side effects should you be aware of?
More serious side effects are much rarer, affecting between 1 in 1000 and 10,000 men taking sildenafil. These can include:
Stroke or mini-stroke
Seizures
Dizziness
Irritability
Eye disorders affecting blood flow and vision
Deafness
Heart problems (including abnormal rhythm and sudden cardiac death)
Nose or throat swelling
Dry nose
Reduced sensation in the mouth
Severe skin conditions (including Stevens-Johnson Syndrome or Toxic Epidermal Necrolysis)
Bleeding from the penis, blood within the semen
An erection lasting more than 4 hours (priapism)
When should you seek medical advice?
If you’re worried about any of these side effects, seek medical attention. In an emergency, such as if you’re experiencing signs of an allergic reaction, stroke, or heart attack, call 999. If you experience an erection lasting longer than 4 hours, it’s important to seek medical help to avoid lasting damage.
More information on side effects can be found in the patient information leaflet.
Who should not take Sildenafil/viagra?
Sildenafil isn’t suitable for everyone. This ED medication should not be taken by women or anyone with an allergy to the active or non-active ingredients. It should also be avoided by men who:
Are taking nitrates (like amyl nitrite for angina)
Are taking guanylate cyclase stimulator medication (such as riociguat)
Are advised not to have sex due to medical reasons
Have vision loss due to non-arteritic anterior ischaemic optic neuropathy
Have severe liver impairment
Have very low blood pressure
Have had a recent stroke or heart attack
Have a known genetic degenerative retinal disorders such as retinitis pigmentosa
Are taking other PDE5 inhibitor medications
Have total lactase deficiency or glucose-galactose malabsorption
Certain people may be able to take sildenafil is some circumstances but may be at increased risk when taking the medication. This includes men:
With changes to the shape, structure, or function of their penis
With conditions which may predispose them to priapism (such as sickle cell anaemia, multiple myeloma or leukaemia)
Who are taking alpha blockers
Who are taking HIV medications like ritonavir
Who have bleeding disorders or active peptic ulcers
It’s important to discuss the risks vs benefits of taking sildenafil with a healthcare professional in these circumstances.
FAQs.
How long does sildenafil take to work?
Sildenafil takes between 30-60 minutes to work, but it may take longer if you’ve eaten a large meal before taking the medication.
What is the best dose of sildenafil?
The standard dose of sildenafil is 50mg up to once a day as needed. You may need a lower dose if you’re older or have certain medical conditions. If you don’t get the results you’re looking for with 50mg, a healthcare professional may increase your dose to 100mg.
Can you take sildenafil every day?
Yes, you can take sildenafil up to once a day as needed. However, if you’re taking sildenafil every day it may be better to switch to tadalafil daily – this will give you more flexibility around sexual activity.
Does alcohol affect sildenafil?
Alcohol can lower your blood pressure, leading to dizziness or fainting. Sildenafil may make these effects worse, so it’s best to avoid alcohol while taking sildenafil.
What foods should I avoid with sildenafil?
Avoid eating a large, high-fat meal before taking sildenafil as this can slow down how quickly the medication works. Grapefruit juice should also be avoided while taking sildenafil as it can slow down how quickly the body breaks the medication down, increasing the risk of side effects.
How often can you take sildenafil?
You can take one sildenafil tablet up to once a day. For the best effects, aim to take sildenafil around an hour before sexual activity.
What are the side effects of sildenafil?
The most common side effect of sildenafil is a headache. Other side effects are less common, and serious side effects are rare. A full list of the side effects can be found in the patient information leaflet.
Can you overdose on Sildenafil?
Taking doses above the recommended or prescribed maximum can increase the likelihood of side effects, especially those related to reduced blood pressure, dizziness, cardiovascular strain and priapism. You must never exceed the prescribed maximum dose and only take one dose per day.
Can you mix sildenafil with other prescription-only-medications?
Yes, you can take it alongside other medications, though sildenafil is generally taken as and when required. There are some limitations as mentioned in this article and for any concerns please contact your Pharmacist or Doctor to discuss further.
References:
https://www.medicines.org.uk/emc/product/5331/pil
https://www.medicines.org.uk/emc/product/7141/smpc#gref
