Sildenafil: What It Does and How
Sildenafil—you probably know it as Viagra—is a medication that helps with erectile dysfunction and certain lung conditions. It's one of the most prescribed drugs in the world because it works reliably and has been studied more thoroughly than almost any other medication. People use it when they want to improve their sexual response or, in some cases, to help their heart pump blood through their lungs more efficiently.
Here's how your body actually handles it. When you're sexually stimulated, your nerves release a chemical called nitric oxide that triggers a chain reaction. Your body starts producing something called cGMP, which tells the blood vessels in your penis to relax and open up. More blood flows in, and you get an erection. The problem is your body has an enzyme that quickly breaks down cGMP, shutting down the whole process. Sildenafil blocks that enzyme—think of it like jamming a drain so the water stays longer. By slowing the breakdown of cGMP, sildenafil extends and strengthens your body's natural response. The key thing: it only works if you're actually stimulated, because it's amplifying your body's own system, not creating desire from scratch. In lung conditions, the same mechanism relaxes blood vessels in the lungs, improving circulation there too.
Dosage Information
Typical Dose
25-100 mg as needed for ED. 20 mg three times daily for pulmonary hypertension.
Frequency
As needed for ED (30-60 minutes before sexual activity). TID dosing for PAH.
Administration
Oral tablet
Half-Life
3–5 hours
Notes
Requires sexual stimulation to produce erection — does not cause spontaneous erections. Avoid with nitrates (absolute contraindication — dangerous hypotension). Food slows absorption. Grapefruit juice increases drug levels.
Why this matters
PDE5 inhibitor; effects last 4–6 hours from single dose.
Protocol cycle
Where does Sildenafil sit?
See how this peptide compares across all 150 peptides in our database.
Evidence Score
0.73
Compound Data
Molecular Formula
C22H30N6O4S
Molecular Weight
474.60 g/mol
IUPAC Name
5-[2-ethoxy-5-(4-methylpiperazin-1-yl)sulfonylphenyl]-1-methyl-3-propyl-6H-pyrazolo[4,5-d]pyrimidin-7-one
PubChem CID
135398744Potential Side Effects
Sildenafil discussions
Quick Facts
- Administration
- Oral tablet
- Typical Dose
- 25-100 mg as needed for ED. 20 mg three times daily for pulmonary hypertension.
- Frequency
- As needed for ED (30-60 minutes before sexual activity). TID dosing for PAH.
- References
- 0 curated + 47 from PubMed
- Clinical Trials
- 50 registered
- Evidence Score
- 0.7 / 100
Frequently Asked Questions about Sildenafil
What is Sildenafil?
Sildenafil (Viagra/Revatio) is a phosphodiesterase type 5 (PDE5) inhibitor FDA-approved for erectile dysfunction and pulmonary arterial hypertension. It is one of the best-selling pharmaceuticals in history with one of the largest clinical evidence bases of any drug — thousands of controlled trials across ED pulmonary hypertension altitude sickness and various investigational applications. While technically a small molecule rather than a peptide sildenafil is fundamental to the sexual health pharmacology landscape and serves as the benchmark against which newer sexual health peptides are compared.
How does Sildenafil work?
Sildenafil inhibits PDE5 — the enzyme that breaks down cyclic GMP (cGMP) in vascular smooth muscle. In the penis sexual stimulation triggers nitric oxide release from cavernous nerves which activates guanylate cyclase producing cGMP. cGMP causes smooth muscle relaxation in the corpora cavernosa increasing blood flow and producing erection. By inhibiting PDE5 sildenafil prevents cGMP breakdown prolonging and enhancing the natural erectile response to sexual stimulation. The critical distinction from bremelanotide is mechanism dependency — sildenafil requires sexual stimulation to work because it amplifies the natural NO/cGMP pathway rather than generating desire de novo. In pulmonary hypertension the same mechanism reduces pulmonary vascular resistance through PDE5 inhibition in pulmonary arterial smooth muscle.
What is the recommended dosage for Sildenafil?
The typical dose is 25-100 mg as needed for ED. 20 mg three times daily for pulmonary hypertension.. As needed for ED (30-60 minutes before sexual activity). TID dosing for PAH.. Administration: Oral tablet. Requires sexual stimulation to produce erection — does not cause spontaneous erections. Avoid with nitrates (absolute contraindication — dangerous hypotension). Food slows absorption. Grapefruit juice increases drug levels.
What are the side effects of Sildenafil?
Headache (common). Facial flushing (common). Dyspepsia (common). Visual disturbances — blue tinge (uncommon). Hypotension especially with nitrates (serious — avoid combination). Priapism (rare but requires urgent treatment)
What is the Sildenafil cycle protocol?
Sildenafil is typically cycled as needed. No cycling protocol; taken PRN or continuous TID
Questions reflect common community inquiries. This is not medical advice.