Sildenafil
Viagra
Sildenafil (Viagra) is a hormonal & sexual research compound. PDE5 inhibitor, same target as tadalafil but far shorter acting and more selective for PDE5 over PDE11 — which is why it causes less back and muscle ache and more visual disturbance (PDE6 crossover).
Sildenafil quick facts
| Reported research dose | 25–100mg as needed |
| Route | Oral |
| Frequency | 1x when used · As needed |
| Half-life | ~4 hours |
| Forms | Oral |
| Evidence level | The original PDE5 randomised-trial dataset |
Shorter and sharper than tadalafil, and genuinely blunted by a heavy meal in a way tadalafil isn't. Blue-tinged vision is a benign PDE6 effect. ⚠️ Never with nitrates.
How Sildenafil works
PDE5 inhibitor, same target as tadalafil but far shorter acting and more selective for PDE5 over PDE11 — which is why it causes less back and muscle ache and more visual disturbance (PDE6 crossover).
Proposed benefits
Researched for libido, hormonal signaling and reproductive / sexual function.
✅ Clinically validated
- Approved with extensive randomised data for erectile dysfunction and, at different dosing, for pulmonary arterial hypertension. Efficacy in ED is around 70% across trials.
📊 Correlative data
- Vast real-world use over 25 years. The safety profile is exceptionally well characterised, and the one absolute rule is unchanged: never with nitrates, where the combination can cause fatal hypotension.
🧪 Theoretical / extrapolated
- A PDE5 inhibitor — it prevents breakdown of cGMP, amplifying the nitric-oxide signal that relaxes vascular smooth muscle.
- It amplifies an existing signal rather than creating one, which is why arousal is still required and why it does nothing for desire. Cross-reactivity with PDE6 in the retina explains the blue-tinted vision some users report.
These tiers tell you how much human evidence exists — not how well something works. This is the research space, and most of what’s in here is new rather than disproven. Something sitting at “theoretical” usually means nobody has funded the trial, not that the trial was run and failed.
The trap runs the other way too: something can be clinically validated and still do very little for you specifically. A statistically significant result in a study population is not a promise about your body.
- ✅ Clinically validated — human randomised trials or meta-analyses support it. The strongest footing available.
- 📊 Correlative — observational or epidemiological data. Suggestive, and genuinely useful for direction, but it cannot establish cause.
- 🧪 Theoretical / mechanistic — the mechanism is understood and often demonstrated in cells or animals, and the human trial doesn’t exist yet. Unproven is not the same as ineffective. Plenty of what’s standard practice today sat here five years ago.
✗ is a safety flag, not a grade. Where you see it, the concern is harm — not a disappointing trial. A compound tested for one purpose and found not to help there can still be worth studying somewhere else, so a negative result never gets rendered as a cross. It sits alongside the tier, because something can be both well-studied and genuinely risky.
My job is to tell you which one you’re looking at, and let you make the call. Grading something low isn’t me dismissing it — it’s me refusing to oversell it. This is the research space, and being able to reason forward from a mechanism matters as much as waiting for the trial.
Sildenafil — safety, predicted from mechanism
Much of this compound class has never been through a human safety trial. Rather than say nothing — or print a generic warning — this is what its known mechanism predicts could go wrong, and what you can do about it. Predictions are labelled as predictions.
What the mechanism predicts
Derived from what this molecule does, not from a trial.
- These inhibit phosphodiesterase type 5, so cGMP persists and smooth muscle relaxes — vasodilation. The predicted problems are all the same effect in the wrong place: headache, flushing, nasal congestion and a fall in blood pressure.
- Tadalafil's long half-life (~17.5 h) means its effects — good and bad — persist far longer than sildenafil's. That is why daily low-dose tadalafil exists and why a mistake with it lasts longer.
What has actually been reported
- Extremely well characterised — these are among the most-prescribed drugs in the world. Headache, flushing, dyspepsia and nasal congestion are common and dose-dependent.
- Rare but serious: sudden hearing loss, and non-arteritic anterior ischaemic optic neuropathy (NAION) — sudden painless vision loss in one eye. Both are reasons to stop immediately and seek care.
- Priapism — an erection lasting over four hours — is a medical emergency, not something to wait out. Delay causes permanent damage.
How to reduce the risk
Each of these follows from the same mechanism as the prediction.
- Start at the low end. The dose-response for side effects is steeper than for benefit.
- Alcohol and these both lower blood pressure; the combination is the usual cause of feeling awful on a normal dose.
What it does to your bloodwork
A fact about the assay, not a guess about the drug.
- Nothing routine. Blood pressure is the measurement that matters and it is not a lab.
Don't run this if
- You take any nitrate — including recreational 'poppers' (amyl nitrite). The combination causes a catastrophic drop in blood pressure and is the one genuinely lethal interaction in this class.
- You take an alpha-blocker, without a prescriber managing the timing.
- You have significant cardiovascular disease or have been advised against sexual activity for cardiac reasons.
Not medical advice. If you take prescription medication or have a diagnosed condition, check this with a pharmacist or doctor.
Where to get Sildenafil
Buy Sildenafil at AlgoRx →Sildenafil — interference & stacking
Predicted from mechanism, not from an interaction study. There are no trials of these combinations — what follows is what the biology implies, so treat it as a reason to watch something, not as a finding.
What Sildenafil moves on your bloodwork
These are the markers this compound is expected to move, and which direction. Knowing that in advance is mostly about NOT panicking: some of these moving is the compound working.
- Complete Blood Count (CBC) with Differential — ↑ expected to rise
Haematocrit and haemoglobin rise — androgens stimulate erythropoiesis. This is the most reliably predictable movement of any compound in the Vault.
What to do: This is the number that decides whether you keep going. Baseline and every 3 months. Dehydration on the draw day inflates it, so hydrate normally or you will chase a false reading. - Total Testosterone — ↑ expected to rise
Expected. Trough vs peak matters enormously — the same protocol reads completely differently depending on when you drew.
What to do: Draw at the same point in the cycle every time or the trend is noise. - LH & FSH — ↓ expected to fall
Suppressed by negative feedback. This is the mechanism, not a side effect — and it is why exogenous androgen shuts down your own production.
What to do: Relevant if fertility matters to you. Worth knowing before, not after. - Estradiol, Sensitive (LC/MS-MS) — ↑ expected to rise
Aromatisation converts a fraction to estradiol, and it rises with the androgen. Use the sensitive (LC-MS/MS) assay — the standard immunoassay is unreliable in men and produces numbers people then medicate.
What to do: If you are reading estradiol in a man, the assay choice matters more than the result. - SHBG (Sex Hormone-Binding Globulin) — ↓ expected to fall
Falls with androgen exposure, which raises the free fraction — so free testosterone can climb faster than total.
What to do: Read total and SHBG together; total alone understates what changed. - Lipid Panel (Cholesterol, HDL, LDL, Triglycerides) — ↓ expected to worsen
HDL falls, sometimes markedly. Oral 17-alpha-alkylated compounds do this far more aggressively than injectable esters.
What to do: Baseline and 12 weeks. ApoB is the better long-term read than LDL-C. - PSA (Total + Free + % Free) — ↑ expected to rise
Androgens can raise PSA modestly. It does not create prostate cancer that wasn't there, but it can unmask it.
What to do: Baseline before starting matters — without it, a later number has nothing to be compared against.
- Which compounds push the same lever, and why the dose adds up faster than people count
- What blunts it — the stacks that waste your money
- What compounds the risk, so a side effect arrives sooner than any one of them suggests
- Coach Cam's read on running it alongside the rest of your protocol
Get the complete breakdown for Sildenafil — inside the Academy alongside the full interactive Vault.
Unlock in the Academy — $10/mo →- How to work up to it, and when not to
- When to take it, and why that window
- Cycle length
- Time off between cycles
- Fasted or fed, and when in the day
- Coach Cam's personal notes
Get the complete breakdown for Sildenafil — inside the Academy alongside the full interactive Vault.
Unlock in the Academy — $10/mo →Bloodwork to run alongside Sildenafil
Run these before you start, and again after 8–12 weeks. A baseline you didn’t take is one you can never go back for.
| Marker | What it’s watching for |
|---|---|
| Total Testosterone | The baseline you can't reconstruct later |
| Free Testosterone | The fraction that does anything — total alone misleads |
| SHBG (Sex Hormone-Binding Globulin) | Explains a normal total sitting on top of a low free |
| Estradiol, Sensitive (LC/MS-MS) | The other half of the ratio, and the source of most symptoms |
| LH & FSH | Separates a testicular problem from a pituitary one |
The Low T? Rule Out the Reversible Causes First panel covers these in one order — 11 markers, $211.50 with the discount applied.
Check results you already have → · All 102 markers A–Z
Sildenafil — frequently asked questions
What is Sildenafil?
Sildenafil (Viagra) is a hormonal & sexual research compound. PDE5 inhibitor, same target as tadalafil but far shorter acting and more selective for PDE5 over PDE11 — which is why it causes less back and muscle ache and more visual disturbance (PDE6 crossover).
Is the full Sildenafil protocol on this page?
The reported research dose is on this page, along with how Sildenafil works and the evidence behind it. The protocol — how to work up to it, frequency, cycle length, time off, what not to stack it with and Coach Cam's notes — is inside the Academy.
What is the half-life of Sildenafil?
Sildenafil has an approximate half-life of ~4 hours, which is part of what determines how often it's dosed.
What's the evidence behind Sildenafil?
Current evidence level: The original PDE5 randomised-trial dataset. Sildenafil is offered for research purposes only and is not an approved medicine.
Want Coach Cam's exact Sildenafil protocol?
Dosing schedules, stacking, cycle timing and my personal notes live inside the Academy — plus the full interactive Vault of 237 compounds & 350 supplements.
Join the Academy — $10/mo →What Sildenafil is used for
Sildenafil appears under 1 goal in the Vault’s goal router, grouped by the mechanism it works through rather than by how much trial evidence exists. Each link opens that pathway in full, with the alternatives beside it and the bloodwork that tests it.