Cialis vs Viagra: What’s the real difference?

Viagra or Cialis — which one is right for you? Both are trusted treatments for erectile dysfunction (ED), but they work in slightly different ways. From how fast they take effect to their duration of action, choosing between them often comes down to your lifestyle and personal preference.

Viagra vs Cialis comparison overview

How Cialis and Viagra work in the body

Both Viagra (sildenafil) and Cialis (tadalafil) belong to a class of ED medications called PDE5 inhibitors. They work in essentially the same way in the body to treat ED, though there are certain pharmacological key differences to consider.

Tadalafil vs Sildenafil: mechanism explained simply

The main mechanism for Cialis and Viagra is the inhibition of the enzyme phosphodiesterase type 5, or PDE5. To understand this, let’s analyse the physiological cascade of sexual arousal.

Nitric oxide release
When a man is sexually aroused — by touch or psychologically — nitric oxide (NO) is released from the nerve endings and endothelial cells that line the blood vessels of the penis. NO is a local signalling molecule that will initiate a cascade of biochemical events.

Activation of guanylate cyclase
NO activates the enzyme guanylate cyclase that converts GTP (guanosine triphosphate) into cyclic GMP (cGMP), and it is an essential regulator of contraction and relaxation in smooth muscle cells, and thus is essential for the induction and maintenance of erection.

Smooth muscle relaxation and blood flow
The high level of cGMP relaxes smooth muscle tissue of the corpus cavernosum and penile arteries. This laxity forces the blood vessels to expand, vastly speeding up blood supply to the penis. The result is a sufficient erection for sexual activity.

Role of PDE5
Naturally, PDE5 cleaves cGMP, eventually stopping the erection. When PDE5 is inhibited by tadalafil or sildenafil, cGMP is less easily broken down, preventing smooth muscle relaxation from ending and therefore the erection from ending.

Important clinical note
No drug has an effect on libido, nor on sexual desire. Sexual stimulation is still needed to induce NO release. PDE5 inhibitors do not induce an erection in the absence of sexual stimulation.

System-wide effects and safety considerations
Although the primary mechanism of action is in the penis, the PDE5 inhibitory process is also exerted on blood vessels throughout the body. This overall effect is a part of what can account for the side effects you’ll experience, such as flushing, headache, stuffy nose or very small changes in blood pressure. For men with preexisting cardiovascular problems, that’s why a patient should be evaluated by a healthcare professional.

Pharmacokinetic distinctions
Sildenafil is faster when taken on an empty stomach, with a shorter duration of action (4–6 hours). Tadalafil has a slower onset in some cases but lasts for more than 36 hours, which is more suitable for spontaneous sexual activity.

In short, PDE5 inhibitors function through elevating the body’s natural erectile response by maintaining cGMP to facilitate smooth muscle relaxation and blood flow, not creating arousal on demand like other erectile dysfunction medications. Realising this helps make sense of why timing, sexual stimulation and cardiovascular well-being all matter for the impact of Cialis and Viagra.

Impact of ED medications on blood flow and erections

The efficacy of ED pills like Cialis and Viagra relies on cardiovascular health because erections depend on an exact balance between blood flow and vascular activity. An erection happens when arterial blood flows quickly into the corpora cavernosa, the sponge-like tissue of the penis, and venous outflow is temporarily limited. Any disease that interrupts circulation can decrease drug efficacy.

There are several possible causes for differentials in response to treatment.

Hypertension: An upswing in blood pressure over the long term might cause damage to vessels and reduce their ability to relax, which prevents the erectile bodies from becoming very swollen.

Diabetes: High blood sugar levels can damage nerves (neuropathy), as well as small blood vessels, which may lower the sensitivity of PDE5 inhibitors.

Obesity, Metabolic Syndrome: Having an excessive weight and its accompanying changing metabolic parameters can interrupt nitric oxide signalling, leading directly to decreased response to ED drugs.

Lifestyle factors: Smoking in adults, high cholesterol levels and being sedentary may all reduce blood flow to the penis.

By improving cGMP levels, Cialis and Viagra help solve some of these vascular problems by improving smooth muscle relaxation as well as blood inflow through your arteries. Such a situation is in effect making sex happen to many men, many men who would otherwise find it impossible to achieve or sustain an erection, a reality.

Which lasts longer: Cialis or Viagra?

The most noticeable difference between the two medicines is how long they last.

Viagra (sildenafil) is typically effective for around 4 to 6 hours, meaning it needs to be taken with a clearer plan around sexual activity.

Cialis (tadalafil), on the other hand, unlike Viagra, can remain effective for up to 36 hours, which is why it’s often referred to as the “weekend pill”. Its longer duration allows for greater spontaneity, as sexual activity does not need to be timed precisely. Many men find this extended window more convenient and less subject to performance pressure.

Cialis vs Viagra side effects comparison

Cialis and Viagra share a similar side effect profile since both are PDE5 inhibitors working through the same biological mechanism. Still, there are some differences in frequency and severity of certain side effects due to their distinct chemical structures and duration of action.

Common side effects

Tadalafil and sildenafil are generally well tolerated, but as with all male erectile dysfunction medications, these can also have side effects as a result of systemic effects acting on blood vessels and smooth muscle. Knowing such differences can allow men to predict reactions and select the best medication.

Headache

Headaches are the most common side effect reported for both ED medications, occurring in around 10-15% of users. They are thought to result from vasodilation in cerebral blood vessels. It is usually mild to moderate, and it normally resolves spontaneously or with simple analgesics.

However, the incidence of more severe cluster or migraine-like headaches is higher with sildenafil, affecting up to 25% of men treated for sexual dysfunction. [4]

Flushing

They can both cause facial redness, warmth or even a feeling of heat in the chest. This is because the vessels dilate, increasing blood flow locally to this area. Flushing is usually brief and goes away after a few hours. The incidence of this side effect is observed to be a bit higher with sildenafil compared to tadalafil. [5]

Indigestion (Dyspepsia)

Inhibitors of PDE5 can gently relax the lower oesophageal sphincter, which may be responsible for heartburn or gastric pain. Men are recommended to avoid high-fat meals about the time when Viagra takes place, which might worsen this effect.

Nasal congestion

When there’s increased blood flow within the nasal passages of the nose, it results in a stuffy or runny nose. This side effect is usually mild enough that you don’t need to stop taking it.

Muscle pain and back pain

More common with Cialis (tadalafil) as a result of its longer half-life and systemic smooth muscle effects. [6] Typically mild, resolves in 24–48 hours. A potentially underlying mechanism is PDE5 inhibition in skeletal muscle blood vessels, resulting in temporary discomfort.

Visual disturbances

Blurred vision (little blur) or changes in colour perception (blue tinge) are common with Viagra (sildenafil). Otherwise, this is seldom due to mild inhibition in the retina of PDE6. The symptoms are typically brief, falling off quickly—only a few hours after onset.

Other less common side effects

Sudden dizziness or lightheadedness brought on by falling blood pressure. Mild fatigue. Gastrointestinal upset.

Comparative notes

Cialis may be favoured by men who are sensitive to visual disturbances, while Viagra may be avoided in men prone to muscle pain. Timing and variation in dosage can minimise side-effects: for instance, taking Viagra on an empty stomach might lower indigestion and delay its onset.

Effects of blood pressure and safety warnings

Both Generic Viagra (sildenafil) and Cialis (tadalafil) exert mild decreases in blood pressure. This effect is relatively small for most healthy men, but it is clinically significant in men with cardiovascular disease or on medications that reduce blood pressure.

Key precautions:

• Do not use with nitrate medications (e.g., nitroglycerin for angina). The two together can lead to acute, life-threatening hypotension. 
• Keep an eye on hypertension medications, if you are on alpha-blockers or antihypertensive medications, as the combination can cause dizziness, fainting and falls. 
• If the erection takes more than 4 hours (priapism), you should seek urgent medical attention (A&E), and the damage can be permanent if left untreated. Such medications should not be used until after the man's prior experience with a heart attack, stroke, unstable heart disease, or severe liver impairment.

Rare but crucial dangers

• Acute vision loss: most commonly in men who have underlying eye problems. 
• Sudden hearing loss: Although it’s very rare, medicines like sildenafil (Viagra), tadalafil (Cialis) and vardenafil (Levitra) have occasionally been linked to sudden hearing problems. Some men have reported a rapid loss of hearing in one ear (so-called "Viagra deafness), sometimes with ringing (tinnitus) or dizziness, usually within a day of taking the tablet. [6]
• Severe hypotension, particularly when combined with nitrates.

Bottom line: Although these medications are generally safe with an appropriate prescription, in men with cardiovascular risk factors or when they are on drugs that interact with other medications, careful observation is needed.

Cialis and Viagra cost in the UK

The Cialis vs Viagra price in the UK depends on whether the medicine is prescribed on the NHS or obtained privately, and whether you choose a branded product or generic versions.

For men eligible for NHS treatment, the standard NHS prescription charge applies (unless exempt). However, many men obtain ED medication privately, where prices vary depending on the brand, strength and quantity supplied.

In general, branded Viagra and Cialis tend to be more expensive than generic sildenafil and tadalafil. Prices vary depending on the dose and pack size.

Which is better for erectile dysfunction: Cialis or Viagra?

Neither Cialis nor Viagra can be definitively said to be "better"; both are highly effective PDE5 inhibitors with similar success rates of 70–85% in the treatment of erectile dysfunction. Which you choose depends on your individual preferences, lifestyle and how your body responds to each medication. [2, 3]

Cialis is ideal for men who prefer spontaneity and longer-lasting effects (up to 36 hours), or for those who are sexually active frequently. [1]

Viagra, on the other hand, is better suited to those who prefer shorter-acting medication (4–6 hours) and want to time sexual activity more precisely. [2]

Some men find one medication more effective or better tolerated than the other due to variations in metabolism and sensitivity to side effects. Your doctor can help you determine which option best suits your needs to treat ED. If one medication doesn't work well for you, it is perfectly reasonable to try the alternative.

Who Should Avoid Cialis or Viagra?

Cialis (tadalafil) and Viagra (sildenafil) are two effective medications for erectile dysfunction treatment, but not appropriate for everyone. Justifications to refrain from using it include:

Take nitrate drugs:

Blood pressure medications for chest pain (eg, nitroglycerin, isosorbide mononitrate) can interact destructively, leading to a dramatic drop in blood pressure.

Just experienced a heart attack or stroke:

Men who recently experienced or have unstable cardiovascular disease should not use these oral ED medications without a specialist’s approval.

Have severe liver or kidney disease:

Significantly impaired liver or kidney function can affect how these medications are metabolised and eliminated from the body, potentially causing dangerous accumulation and increased side effects.

Have uncontrolled blood pressure:

If blood pressure is very high or very low, both increase the risk of complications.

Take certain interacting medications:

Alpha-blockers for enlarged prostate or high blood pressure, certain antifungal medications (ketoconazole, itraconazole), HIV protease inhibitors (ritonavir, saquinavir), some antibiotics (clarithromycin, erythromycin), and riociguat (for pulmonary hypertension) can interact with Cialis or Viagra, requiring dose adjustments, careful timing, or alternative treatments.

Anatomical deformities:

Caution is advised in patients with conditions like Peyronie's disease or penile fibrosis, as an erection may be painful or medically complicated.

Other warning:

Men who are treated for benign prostatic hyperplasia (BPH) or pulmonary arterial hypertension (PAH) must consult healthcare providers. Dosage and safety standards vary.

Can you switch between Cialis and Viagra?

Switch out is possible, but you need:

Taking neither medicine on the same day, taking into account time, the dose of therapy and drug interactions. Using a healthcare provider for personalised advice.

Patient example: For an extended duration of action, Mark, 60, replaced Viagra with Cialis. He sought advice from his clinician in order to avoid low blood pressure risks.

Lifestyle considerations: Avoid use of recreational drugs with ED drugs. It could harm blood flow and the quality of an erection, so limit alcohol. Food intake affects the onset of Viagra; Cialis is less sensitive.

Frequently asked questions

Both medications are the most widely prescribed and used to improve male sexual function. This means they are the subject of many disputes and discussions. Here are some frequently asked questions we addressed:

Is Cialis stronger than Viagra?

No, the strength is similar. The biggest difference is duration.

Does Cialis raise blood pressure?

No, both can cause a slight decrease in blood pressure.

Can you take Cialis daily?

Yes, Cialis daily (Tadalafil daily) in its low dose (2.5–5mg) is approved for daily use. This also sets Cialis apart from Viagra, which is intended for on-demand use only.

Which is cheaper in the UK?

Generic medications are significantly cheaper than branded versions. Generic sildenafil typically costs £1-3 per tablet, whilst generic tadalafil ranges from £1.50-4 per tablet through online pharmacies or private prescriptions. Branded Viagra costs considerably more at £5-10+ per tablet, and branded Cialis prices go up to £6-12+ per tablet.

Can you combine Viagra and Cialis?

No, combining increases the risk of low blood pressure.

How do Cialis and Viagra affect sexual performance?

 They increase erectile function, not libido.

Conclusion

The Cialis vs Viagra battle is more about preference, convenience, and body positivity versus superior medicine. Both medications are effective alternatives for treating erectile dysfunction.

Sources

[1] Eardley I, et al. Patient preference for tadalafil or sildenafil. Eur Urol. 2005;47(6):839-846. https://pubmed.ncbi.nlm.nih.gov/15882756/

[2] Goldstein I, et al. Oral sildenafil in erectile dysfunction. N Engl J Med. 1998;338:1397-1404. https://pubmed.ncbi.nlm.nih.gov/9580646/

[3] Porst H, Burnett AL, Brock G, et al. Efficacy of tadalafil once daily in men with erectile dysfunction: results of a multicenter, randomised, double-blind, placebo-controlled trial. Eur Urol. 2006;50(2):351-359. https://pubmed.ncbi.nlm.nih.gov/16766116/

[4] Lin GY, Lee JT, Peng GS, Yang FC. Sildenafil can induce the onset of a cluster headache bout. Can Urol Assoc J. 2014;8(5-6):E378-E380. doi:10.5489/cuaj.1736. https://cuaj.ca/index.php/journal/article/view/1736

[5] Gong, B., Ma, M., Xie, W. et al. Direct comparison of tadalafil with sildenafil for the treatment of erectile dysfunction: a systematic review and meta-analysis. Int Urol Nephrol 49, 1731–1740 (2017). https://link.springer.com/article/10.1007/s11255-017-1644-5

[6] Barreto MA, Bahmad F Jr. Phosphodiesterase type 5 inhibitors and sudden sensorineural hearing loss. Braz J Otorhinolaryngol. 2013;79(6):727-733. doi:10.5935/1808-8694.20130133. https://www.sciencedirect.com/science/article/pii/S1808869415302238?via%3Dihub