Sildenafil
Also known as: Sildenafil, Viagra, Sildenafil citrate, Revatio
The short-acting counterpart to tadalafil — better for a single occasion, worse for everything tadalafil is actually used for here.
Substance family
Medications for blood pressure, lipids and glucose. They appear here because these are exactly the markers most anabolic compounds push in the wrong direction.
Effects on
Which outcomes this substance acts on — descriptive, not a recommendation.
Strain profile
Where this substance is most likely to hit — a rough orientation, individually dependent on dose, duration and predisposition.
This substance works against
Dosing & protocols by goal
Rough orientation ranges as reported in harm-reduction literature — not an individual treatment plan. Doses are individual and open-ended; frequency depends on the ester or half-life.
Erectile function (approved indication)
MedicalDose
25–100 mg
Frequency
As needed, 30–60 min beforehand
Cycle length
—
Start at the lower end. A heavy or fatty meal delays absorption considerably — this is the practical difference from tadalafil, which is largely unaffected by food.
Pulmonary hypertension (approved indication)
MedicalDose
20 mg, 3× daily
Frequency
3× daily
Cycle length
Ongoing, medically supervised
Marketed as Revatio for this indication. The same mechanism that widens vessels in the penis widens them in the lungs.
Daily use for blood pressure or vascular health
Not a recommendationDose
—
Frequency
—
Cycle length
—
The four-hour half-lifehalf-lifeHow long it takes for half the substance to leave the body — it determines dosing frequency, not duration of effect. makes daily dosing impractical for continuous effect. Where a PDE5 inhibitor is wanted for ongoing cardiovascular benefit, tadalafil at 2.5–5 mg daily is the sensible choice — that is why it, not sildenafil, appears throughout the rest of this site.
Side effect & countermeasure
Typical problems and what you can do to reduce harm — at a glance. Does not replace medical monitoring.
Problem
Nitrates are an absolute contraindication
Countermeasure
Combining a PDE5 inhibitor with nitrate medication — nitroglycerin, isosorbide, and amyl nitrite 'poppers' — can cause a catastrophic drop in blood pressure. This is not a caution to weigh; it is a hard rule. Poppers are the relevant version of this for a recreational context and the combination has killed people.
Problem
Additive blood-pressure lowering
Countermeasure
Alongside telmisartan, amlodipine, lisinopril or citrulline the drop adds up. Usually mild, but real — measure rather than assume, and be careful standing up quickly. Alpha blockers are the class where the interaction is strongest.
Problem
It does not fix a hormonal problem
Countermeasure
Erectile difficulty on cycle frequently has a hormonal cause: high prolactinprolactinA pituitary hormone that, when elevated, causes low libido, erectile problems and breast tissue growth. from 19-nor compounds, estradiolestradiolThe main estrogen — needed in men too, and damaging in both directions when out of range. crushed too low by an aromatase inhibitoraromatase inhibitorA drug that blocks the conversion of testosterone to estradiol., or an inadequate testosterone base. A PDE5 inhibitor works on the vascular step and will mask any of those without addressing them. Measure prolactin and estradiol before treating the symptom indefinitely.
Problem
Choosing it when tadalafil fits better
Countermeasure
Sildenafil lasts about four hours, tadalafil around 17.5 and remains effective for a day or more. For spontaneity, and for the low-dose daily use that gives ongoing vascular benefit, tadalafil is simply the better tool. Sildenafil's advantage is a stronger acute effect at peak and lower cost.
Problem
Visual side effects
Countermeasure
A blue tinge to vision and light sensitivity occur because sildenafil has some activity at PDE6 in the retina. It is dose-dependent, temporary and harmless — but worth knowing, as it can be alarming and it is more pronounced than with tadalafil.
Overview
Sildenafil is the original PDE5 inhibitor and the better-known name, but on this site tadalafil appears far more often. That is not an oversight — it reflects a real difference in what each is suited to.
Mechanism of Action
Sexual arousal releases nitric oxide in the erectile tissue, which raises cGMP, which relaxes smooth muscle and allows blood to fill the tissue. PDE5 is the enzyme that breaks cGMP back down.
Inhibiting PDE5 means cGMP persists, so the vasodilation is stronger and lasts longer. Arousal is still required — the drug amplifies a signal rather than creating one.
The same enzyme sits in blood vessels elsewhere, including in the lungs, which is why sildenafil is also approved for pulmonary hypertension and why a mild systemic blood-pressure reduction comes with it.
Sildenafil or Tadalafil
The practical differences:
| Sildenafil | Tadalafil | |
|---|---|---|
| Half-life | ~4 hours | ~17.5 hours |
| Effective window | 4–6 hours | 24–36 hours |
| Food effect | Fatty meals delay it noticeably | Largely unaffected |
| Daily low-dose use | Impractical | 2.5–5 mg, established |
| Visual side effects | More common | Rare |
| Muscle and back ache | Rare | More common |
For a single occasion, sildenafil at peak is somewhat stronger and cheaper. For everything else — spontaneity, daily low-dose use, ongoing blood-pressure and vascular benefit — tadalafil wins clearly. That is why the rest of this site references tadalafil.
The Diagnostic Trap
Erectile problems during a cycle are common, and a PDE5 inhibitor makes them go away. That is precisely the risk.
The usual causes are hormonal rather than vascular:
- Elevated prolactin from nandrolone or trenbolone — cabergoline is the lever, not a PDE5 inhibitor
- Estradiol crushed too low by an aromatase inhibitor — the fix is less AI, not more sildenafil
- An inadequate testosterone base alongside a 19-nor compound
- Insufficient DHT activity, where mesterolone supplies the androgenic tone
Sildenafil covers all of these without touching any of them. Someone taking it for months while prolactin runs high has a treated symptom and an untreated cause. Measure prolactin and estradiol first.
Side Effects & Risks
- Headache, facial flushing
- Nasal congestion
- Blue tinge to vision, light sensitivity
- Indigestion
- Dizziness and low blood pressure, especially combined with other vasodilators
- Priapism — an erection lasting over four hours is a medical emergency, not something to wait out
- Rare reports of sudden hearing loss
Blood Work & Monitoring
- Prolactin — before treating erectile problems as vascular
- Estradiol (sensitive assay) — the other common hormonal cause
- Total and free testosterone
- Blood pressure — if other antihypertensives are in use
Legal status by region
Regulation differs considerably between jurisdictions and changes over time. This is a rough orientation, not legal advice — check the rules that apply where you are.
| Region | Regulatory status |
|---|---|
| United States | Prescription-only medicine |
| EU / UK | Prescription-only; available from pharmacies without prescription in some countriesThe UK permits pharmacy sale after a consultation. |
| Most other jurisdictions | Prescription-only; availability varies widely |
| Competitive sport | Not prohibited |