Ever wondered what actually happens inside your body when you get an erection? It’s not magic—it’s chemistry. And understanding that chemistry is the key to grasping why medicines like tadalafil (the active ingredient in daily 5mg tablets) work so well for erectile dysfunction.
At the heart of it all is a tiny molecule called nitric oxide. Think of it as your body’s “go” signal for blood flow. When that signal works properly, everything flows smoothly. When it doesn’t, erectile dysfunction can happen. This guide breaks down the science in plain English, explains what goes wrong, and shows how PDE5 inhibitors—including tadalafil—fix the problem.
Table of contents
- Five key takeaways
- The Nitric Oxide pathway: Your body’s erection blueprint
- What goes wrong: Erectile Dysfunction explained
- How PDE5 inhibitors were discovered
- Tadalafil and daily dosing: A different approach
- Why daily tadalafil works better for some men
- How tadalafil fits into the PDE5 class
- The bottom line
- References
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Five key takeaways
- Erections run on chemistry, not “willpower”. Nitric oxide (NO) is the key messenger that tells penile blood vessels to relax so blood can flow in and stay there.
- NO flips on the “cGMP signal”. NO triggers an enzyme (sGC) to make cGMP, which lowers calcium in smooth muscle and helps the erectile tissue relax and fill.
- PDE5 is the off-switch. PDE5 breaks down cGMP; if cGMP disappears too fast (or NO is low), the erection fades early—classic erectile dysfunction.
- PDE5 inhibitors keep the signal alive. Medicines like sildenafil, tadalafil, and vardenafil block PDE5, so cGMP hangs around longer and erections are easier to get and maintain (with arousal still needed).
- Daily tadalafil is about steadiness and spontaneity. Because it lasts much longer, a 5mg daily dose can provide “background support” without timing sex, and may help confidence by reducing performance pressure.
The Nitric Oxide pathway: Your body’s erection blueprint
Step 1: Arousal kicks off the signal
When you’re sexually aroused—whether from touch, thoughts, or visual cues—your nervous system springs into action. Nerves in your penis and pelvic area fire up, sending signals that say, “Time to get things moving.”
Step 2: Nitric Oxide gets made and released
Here’s where nitric oxide enters the story. An enzyme called nitric oxide synthase (NOS) uses an amino acid called L-arginine to manufacture nitric oxide [1]. This NO is released from two places:
- Nerves in the penis (called nitrergic nerves).
- The lining of blood vessels (the endothelium).
Think of nitric oxide as a chemical messenger. It’s tiny, it travels fast, and it has one job: tell the smooth muscle in your penis to relax.
Step 3: Nitric Oxide unlocks the “cGMP factory”
Nitric oxide diffuses into the smooth muscle cells of the corpora cavernosa—that’s the spongy erectile tissue inside your penis. Once there, it activates an enzyme called soluble guanylyl cyclase (sGC) [1].
This enzyme is like a factory switch. When NO flips it on, the factory starts making a chemical called cGMP (cyclic guanosine monophosphate). cGMP is the actual “relax” instruction for smooth muscle [1].
Step 4: cGMP tells muscle to chill out
cGMP activates a protein called protein kinase G (PKG). PKG’s job is to lower calcium levels inside muscle cells and dial down the signals that tell muscles to contract [1].
Result? The smooth muscle in your penile arteries and erectile tissue relaxes.
Step 5: Blood rushes in, gets trapped—erection happens
When smooth muscle relaxes, two things happen:
- More blood flows in. Relaxed arteries let blood pour into the erectile tissue.
- Blood gets trapped. As the tissue fills and expands, it compresses the veins that normally drain blood out. This is called veno-occlusion. Blood can’t easily escape, so it stays put, and you get a firm erection.
Step 6: The signal fades (and where things go wrong)
Here’s the critical bit: an enzyme called PDE5 (phosphodiesterase type 5) breaks down cGMP. Once cGMP is gone, the “relax” signal stops, smooth muscle tightens again, and the erection softens [1].
This is normal and healthy when you want it to be. But if PDE5 is too active, or if nitric oxide isn’t being made in the first place, cGMP gets broken down too quickly—and you can’t maintain an erection. That’s erectile dysfunction.
What goes wrong: Erectile Dysfunction explained
Erectile dysfunction (ED) happens when the nitric oxide pathway gets disrupted. Common culprits include:
- Low nitric oxide production. Stress, smoking, diabetes, heart disease, and high blood pressure can all reduce NO levels.
- Poor blood flow. Clogged arteries or weak circulation means less blood reaches the penis in the first place.
- Too much PDE5 activity. Some men’s bodies break down cGMP faster than others, making it harder to maintain an erection.
- Psychological factors. Anxiety and depression can interfere with the nerve signals that trigger NO release.
The result is the same: not enough cGMP, not enough smooth muscle relaxation, not enough blood trapped in the erectile tissue. No firm erection.
How PDE5 inhibitors were discovered
The story of PDE5 inhibitors is a brilliant example of accidental discovery in medicine.
Viagra’s origin story is less “slick lab breakthrough” and more “happy accident in a very normal place” [2].
In the early 1990s, Pfizer was testing a compound called sildenafil (UK?92,480) as a potential treatment for angina and high blood pressure. Part of that early research was run through a trial centre in Merthyr Tydfil, where local men volunteered for paid studies during a tough period of industrial decline [2].
The drug didn’t turn out to be a winner for chest pain. But the volunteers reported an unexpected side effect: more frequent, firmer erections. That awkward feedback became Pfizer’s lightbulb moment. Instead of binning the compound, they pivoted, funded dedicated erectile dysfunction studies, and the rest is history [2].
By 1998, sildenafil launched as Viagra — the first approved oral treatment for erectile dysfunction — and it quickly changed how ED was treated (and talked about) worldwide [2].
The success of Viagra sparked a race. Other pharmaceutical companies developed their own PDE5 inhibitors:
- Tadalafil (Cialis) was approved in 2003 [3].
- Vardenafil (Levitra) was approved in 2003 [4].
- Avanafil (Stendra) was approved in 2012 [5].
All of them work the same way: they slow down PDE5, letting cGMP stick around longer and keeping the erection-friendly signal active.
Tadalafil and daily dosing: A different approach
While sildenafil (Viagra) and vardenafil (Levitra) are typically taken as needed—30 minutes to an hour before sex—tadalafil offers something different: daily dosing [6].
Tadalafil has a much longer half-life than other PDE5 inhibitors. This means it stays active in your body for up to 36 hours [6]. Because of this, a low daily dose of 5mg can maintain steady cGMP levels all day long, without needing to time it around sexual activity [6].
Why daily tadalafil works better for some men
- Spontaneity. You don’t have to plan sex. The medication is already in your system.
- Steadier levels. Daily dosing avoids the “spike and crash” of as-needed pills, which can mean fewer side effects.
- Improved blood flow. Over time, consistent cGMP elevation may improve overall penile blood flow and nerve function [6].
- Psychological benefit. Knowing the medication is always working can reduce performance anxiety [6].
How tadalafil fits into the PDE5 class
Tadalafil is part of the PDE5 inhibitor family, but it has some unique traits:
| Feature | Sildenafil (Viagra) | Tadalafil (Cialis) | Vardenafil (Levitra) |
| Half-life | ~4 hours | ~17.5 hours | ~4–5 hours |
| Onset | 30–60 minutes | 30 minutes–2 hours | 25–60 minutes |
| Duration | 4–6 hours | Up to 36 hours | 4–5 hours |
| Daily dosing? | No (as-needed only) | Yes (5mg daily) | No (as-needed only) |
| Food interaction | High-fat meals delay it | Minimal food impact | Minimal food impact |
All three work by the same mechanism—blocking PDE5—but tadalafil’s longer action makes it ideal for men who want consistent, background support rather than a timed dose [6].
The bottom line
Erectile dysfunction isn’t a personal failing—it’s a breakdown in the nitric oxide pathway. PDE5 inhibitors, including tadalafil, fix that breakdown by keeping cGMP around longer, so the “relax and fill” signal stays strong.
Tadalafil’s daily 5mg option is particularly useful because it maintains steady levels without the need to plan ahead. For many men, it’s a game-changer: better spontaneity, fewer side effects, and the confidence that comes from knowing the science is working in your favour.
If you’re considering tadalafil or any PDE5 inhibitor, a confidential consultation with a clinician—like those offered at Medical Mojo—is the best first step. They’ll review your health, check for interactions, and help you find the option that works best for you.
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Disclaimer: This article is for informational purposes only and does not replace professional medical advice.
References
[2] [1] BBC News (2023). How Viagra was discovered in south Wales. Available at: https://www.bbc.com/news/uk-wales-67417111
[3] Drugs.com (2003). Lilly-ICOS announces FDA approval Cialis (tadalafil), new oral erectile dysfunction. Available at: https://www.drugs.com/newdrugs/lilly-icos-announces-fda-approval-cialis-tadalafil-new-oral-erectile-dysfunction-241.html
[5] [1] Drugs.com (2024). Stendra (avanafil) history. Available at: https://www.drugs.com/history/stendra.html
[6] 1] Courier Pharmacy (2024). The journey to once-daily dosing of tadalafil 5mg tablets. Available at: https://courierpharmacy.co.uk/the-journey-to-once-daily-dosing-of-tadalafil-5mg-tablets/
