Introduction
Erectile dysfunction (ED) is the inability to get or keep an erection firm enough for satisfactory sexual activity. It can be caused by physical or psychological factors. Phosphodiesterase type 5 inhibitors (PDE5 inhibitors) are the most common oral treatments for ED. They work by blocking the enzyme PDE5 to improve blood flow to the penis and allow an erection to occur.
This article compares two of the most well-known PDE5 inhibitor medications – sildenafil (Viagra) and tadalafil (Cialis). Sildenafil was introduced in 1998 as the first oral treatment for ED. Tadalafil entered the market in 2003 as a longer-lasting alternative. While the drugs have similarities, they also have some key differences that individuals should understand when considering treatment options for ED.
Mechanism of Action
Sildenafil (the active ingredient in Viagra) and tadalafil (the active ingredient in Cialis) are both PDE5 inhibitors that help treat erectile dysfunction (ED) in men.
PDE5 inhibitors work by blocking the enzyme phosphodiesterase type 5 (PDE5). PDE5 breaks down a substance called cyclic guanosine monophosphate (cGMP), which normally causes the smooth muscles in the penis to relax allowing increased blood flow. When PDE5 is inhibited, cGMP levels build up allowing for increased blood flow into the penis and improved erections.
Both sildenafil and tadalafil have a similar mechanism of action as PDE5 inhibitors. They prevent PDE5 from breaking down cGMP so that blood can flow into the penis and cause an erection in response to sexual stimulation. Although they work in the same way, there are some differences between the two drugs in terms of onset of action and duration of effects.
Effectiveness
Both sildenafil (Viagra) and tadalafil (Cialis) are effective treatments for erectile dysfunction. Clinical trials have found the following efficacy rates:
- Sildenafil: In clinical trials, between 60-80% of men taking sildenafil were able to achieve improved erections. The efficacy of sildenafil is dose-dependent, meaning higher doses are associated with better effectiveness. Doses of 50 mg improved erections in 59% of men, while 100 mg doses were effective for 80% of men.
- Tadalafil: Clinical trials found tadalafil to be effective in 60-81% of men, depending on the dose. With low doses of 2.5-5 mg daily, effectiveness rates were around 50-60%. With on-demand doses of 10-20 mg, efficacy increased to ~70%. Higher doses of 20 mg resulted in improved erections in 81% of men.
Overall, both PDE5 inhibitors demonstrate similar efficacy profiles, with rates generally between 60-80%. Higher doses tend to improve effectiveness for both sildenafil and tadalafil. However, there is substantial individual variation in response. Some men may find one medication more effective than the other.
Onset and Duration
Sildenafil and tadalafil work in similar ways to treat erectile dysfunction but have some differences in onset and duration of effects.
- Sildenafil is absorbed into the bloodstream quicker than tadalafil. It typically starts working in 30-60 minutes. The effects last for approximately 4 hours.
- Tadalafil is slower to be absorbed but can work in as little as 30 minutes for some patients. More commonly, it takes 60-90 minutes to start working. The effects of tadalafil can last up to 36 hours, earning it the nickname “the weekend pill.”
- The longer duration of action for tadalafil gives it an advantage over sildenafil for some patients. Taking a single dose on Friday night provides the ability to be intimate anytime over the weekend without having to plan ahead and take a pill right before sexual activity.
- However, the quicker onset of sildenafil can be preferred if taking a pill right before sex. The shorter duration of action requires less planning around meals that could affect absorption.
- Overall, tadalafil lasts significantly longer but sildenafil acts somewhat faster. Patients should consider their specific needs and preferences when deciding between the two medications.
Side Effects
Sildenafil and tadalafil have some similar side effects, though the rates of occurrence differ.
The most common side effects of sildenafil are headache, flushing, upset stomach, abnormal vision (such as changes in color vision), stuffy or runny nose, back pain, muscle pain, nausea, dizziness, and rash. Headaches occur in around 16% of men taking sildenafil, flushing in 10%, dyspepsia in 7%, abnormal vision in 3%, stuffy nose in 1-10%, and back pain in 2%.
For tadalafil, common side effects include headache, indigestion, back pain, muscle aches, flushing, and stuffy or runny nose. Headaches are reported in around 14% of men taking tadalafil, dyspepsia in 12%, back pain in 6%, myalgia in 5%, flushing in 3%, and nasal congestion in 1-10%.
Overall, headache and flushing appear to be more common with sildenafil, while back pain, muscle aches, indigestion, and stuffy nose are reported more often with tadalafil. However, the differences in side effect rates are generally small. Both medications are typically well tolerated, and side effects are mild and transient. Serious side effects are uncommon with either drug.
Interactions
Both sildenafil and tadalafil can interact with certain medications and affect how the drugs work.
Nitrates
Do not take PDE5 inhibitors with nitrates as the combination can cause a severe drop in blood pressure. Nitrates are used to treat angina (chest pain from heart disease). Medications like nitroglycerin, isosorbide mononitrate/dinitrate should not be taken with sildenafil or tadalafil. Allow at least 24 hours between use of a nitrate and a PDE5 inhibitor.
Alpha-blockers
Using PDE5 inhibitors with alpha-blockers for prostate conditions or high blood pressure can also cause a drop in blood pressure. Examples of alpha-blockers include tamsulosin (Flomax), terazosin (Hytrin), doxazosin (Cardura). Allow at least 4-6 hours between taking an alpha-blocker and a PDE5 inhibitor.
Other interactions
Other drugs that can interact include antifungals like ketoconazole or itraconazole, antibiotics like erythromycin or clarithromycin, and HIV protease inhibitors like ritonavir or saquinavir. Always check for interactions when starting a new medication. Grapefruit juice can also increase the blood levels of sildenafil and tadalafil.
Let your doctor know about all medications, supplements, and herbal products you take to prevent dangerous interactions. Combining PDE5 inhibitors with illegal drugs like “poppers” can lead to severe health consequences.
Food Interactions
Taking sildenafil or tadalafil with food can affect how the medication is absorbed and how quickly it starts working.
- Sildenafil is best absorbed on an empty stomach. High-fat foods can delay absorption and reduce effectiveness. For best results, take sildenafil 1 hour before sexual activity on an empty stomach.
- Tadalafil absorption is less affected by food. It can be taken with or without food. However, taking it with a high-fat meal may delay the onset of action by 1 hour. For fastest action, take tadalafil on an empty stomach.
- Avoid grapefruit and grapefruit juice when taking either medication, as this can increase drug levels and side effects.
- Overall, sildenafil is more sensitive to food interactions than tadalafil. If taking sildenafil, avoid high-fat meals for optimal results. Tadalafil is more flexible in terms of meal timing.
Dosage
Sildenafil and tadalafil are dosed differently. Sildenafil is typically prescribed at doses of 25 mg, 50 mg, or 100 mg to be taken as needed approximately 1 hour before sexual activity. The starting dose is usually 50 mg and the maximum recommended dose is 100 mg. Doses higher than 100 mg do not provide additional effectiveness but may increase side effects.
In comparison, the recommended starting dose for tadalafil is 10 mg taken at least 30 minutes before sexual activity. It may be increased to 20 mg or lowered to 5 mg based on efficacy and tolerability. The maximum recommended dose is 20 mg and doses higher than that are not more effective. Unlike sildenafil, tadalafil is also approved for daily use at doses of 2.5mg or 5mg. This allows more spontaneous sexual activity as it does not need to be taken right before.
Overall, sildenafil is dosed higher on an as-needed basis while tadalafil can be taken at a lower daily dose. Both medications should be started at the lowest dose and titrated based on the individual patient’s response and preferences.
Cost
Sildenafil and tadalafil are both brand name prescription drugs, which means they tend to be more expensive than generic versions. However, prices can vary significantly depending on if you have prescription drug insurance coverage or not.
Without insurance, sildenafil can cost $50-$60 for six 50mg tablets. Tadalafil averages around $400 for thirty 5mg tablets.
With prescription insurance, sildenafil may cost $10-$15 for six 50mg tablets. Tadalafil is often around $30-$35 for thirty 5mg tablets.
Generic versions of sildenafil and tadalafil are now available, which can lower costs even further. Generic sildenafil can be as low as $3 per tablet, while generic tadalafil averages $25-$30 for thirty 5mg tablets.
Many factors affect the cash price, including the pharmacy, dose, quantity, and if you use a prescription discount card. Overall, tadalafil tends to be more expensive than sildenafil. Having prescription insurance or using generic versions can save quite a bit of money. Those without insurance may need to rely on prescription discount cards or pay the full cash price.
Conclusion
Sildenafil (Viagra) and tadalafil (Cialis) are both PDE5 inhibitors used for treating erectile dysfunction (ED). They have similar mechanisms of action and effectiveness.
The main differences are:
- Onset and duration – Sildenafil starts working in 30-60 minutes and lasts for about 4 hours, while tadalafil takes effect in 15-45 minutes and can work for up to 36 hours. Tadalafil offers more flexibility with dosing.
- Side effects – Both can cause headaches, flushing, stomach upset, back pain, muscle aches, and runny nose. However, tadalafil is less likely to cause visual disturbances like blurred vision or blue-tinged vision.
- Food interactions – High-fat meals can delay absorption of sildenafil and reduce effectiveness. Fatty foods do not affect tadalafil as much.
- Dosage – Sildenafil is taken as needed at 25-100 mg, while tadalafil is taken at 10-20 mg daily or 20 mg as needed.
- Cost – Tadalafil is more expensive, especially for daily use. Sildenafil offers a more affordable option.
In summary, while they are similar ED drugs, tadalafil tends to have a longer duration with fewer visual side effects, but is more expensive. Sildenafil is cheaper with a shorter window of action. The choice depends on the patient’s preference, planned sexual activity, other medical history, and affordability.
