Sildenafil citrate review
The default first try — cheap, predictable, heavily studied
Our overall score
Written by J. Porter, MPH
Medically reviewed by A. Vance, MD
Last reviewed
The short version
Sildenafil is the oldest and most-studied ED medication, and generic versions are now the cheapest option on the market. It works well for most people, but its short window and sensitivity to fatty meals mean it requires more planning than tadalafil.
Best for: Anyone starting treatment who wants the lowest cost and the largest body of evidence behind it.
What works
- By far the lowest cost — generic sildenafil is often a few dollars a month
- Nearly 30 years of real-world safety data
- Flexible dosing from 25 mg to 100 mg
- Stocked by essentially every pharmacy
What to watch
- Fatty meals meaningfully delay how fast it works
- The 4–6 hour window forces you to plan around a dose
- Blue-tinged vision and light sensitivity are more common than with avanafil
Get emergency help for these
- An erection lasting more than 4 hours — this can cause permanent damage
- Sudden loss of vision or hearing
- Chest pain during or after sex — tell responders you took a PDE5 inhibitor
At a glance
- Generic name
- Sildenafil citrate
- Brand name
- Viagra
- Drug class
- PDE5 inhibitor
- FDA approved
- 1998
- Typical doses
- 25 mg, 50 mg, 100 mg
- Usual starting dose
- 50 mg as needed, adjusted up or down based on response
- Onset
- 30–60 minutes
- Duration
- 4–6 hours
- Half-life
- ~4 hours
- Effect of food
- A high-fat meal can delay onset by about an hour
- Generic available
- Yes
- Typical cost
- Roughly $0.50–$4 per tablet for the generic with a discount cardChecked July 15, 2026. Prices vary widely by pharmacy — treat as a ballpark, not a quote.
- Also approved for
- Pulmonary arterial hypertension (as Revatio, 20 mg)
How sildenafil works
Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor. Sexual arousal causes nerve endings in the penis to release nitric oxide, which triggers production of a signaling molecule called cGMP. cGMP relaxes the smooth muscle in the arteries of the penis, blood flows in, and an erection results. The PDE5 enzyme breaks cGMP back down.
Sildenafil blocks PDE5, so cGMP sticks around longer and the erection is easier to get and keep. The practical consequence people most often miss: the drug does not create arousal. Without sexual stimulation there is no nitric oxide release, no cGMP, and nothing for sildenafil to preserve. It is an amplifier, not a switch.
Dosing and timing
The usual starting dose is 50 mg taken roughly one hour before sex, and no more than once per day. Prescribers commonly move to 100 mg if 50 mg is tolerated but underwhelming, or down to 25 mg if side effects are bothersome. Older adults and people with significant kidney or liver impairment often start at 25 mg.
- Take it
- About 1 hour before sex, on a relatively empty stomach
- Frequency
- No more than once in 24 hours
- Food
- A heavy, fatty meal delays absorption by roughly an hour
- Alcohol
- Moderate amounts are usually fine; heavy drinking worsens ED and compounds low blood pressure
Side effects
Most side effects come from PDE5 inhibition elsewhere in the body, and they scale with dose. They are typically mild and pass within a few hours.
| Side effect | Roughly how common | Notes |
|---|---|---|
| Headache | Common | The most frequent complaint; usually responds to ordinary pain relievers |
| Facial flushing | Common | Warmth and redness in the face and neck |
| Indigestion / reflux | Fairly common | Sildenafil relaxes the esophageal sphincter |
| Nasal congestion | Fairly common | Blood vessel dilation in the nasal lining |
| Blue-tinged or blurred vision | Uncommon, dose-related | Sildenafil also weakly inhibits PDE6 in the retina; resolves as the drug clears |
| Back pain or muscle aches | Uncommon | More characteristic of tadalafil than sildenafil |
Who should not take sildenafil
Beyond nitrates, tell your prescriber if any of the following apply — several are hard stops and others just require a lower dose:
- Riociguat (Adempas) or another guanylate cyclase stimulator — contraindicated
- Alpha blockers such as tamsulosin or doxazosin — usually workable, but start low and separate the doses
- Strong CYP3A4 inhibitors such as ritonavir, ketoconazole, or clarithromycin — these raise sildenafil levels sharply and call for a 25 mg starting dose
- A heart attack, stroke, or life-threatening arrhythmia in the last six months
- Unstable angina, or angina brought on by sex
- Severe liver impairment, or resting blood pressure that is very low or poorly controlled and high
- A previous episode of NAION (sudden vision loss in one eye)
- Hereditary degenerative retinal disorders such as retinitis pigmentosa
Sildenafil versus the alternatives
Head-to-head trials have generally not shown one PDE5 inhibitor to be dramatically more effective than another. The real differences are practical: how fast it works, how long it lasts, what it costs, and which side effects you personally get.
- Choose sildenafil if cost is the priority and you can plan an hour ahead
- Choose tadalafil if you want a long window or a daily low dose that removes timing entirely
- Choose avanafil if you need speed or sildenafil's visual side effects bother you
A note on “herbal Viagra”
The FDA has repeatedly found supplements marketed as natural ED remedies to contain undeclared prescription drugs — frequently sildenafil itself, sometimes at unpredictable doses. Because the label does not disclose it, a buyer on nitrates has no way to know they are at risk. Treat unregulated ED supplements as the more dangerous option, not the safer one.
Common questions
How long before sex should I take sildenafil?
About an hour is the standard advice. It can begin working in 30 minutes on an empty stomach, but a large or fatty meal can push onset out by roughly an additional hour.
Is generic sildenafil as good as brand-name Viagra?
Yes. Generic sildenafil contains the same active ingredient and must meet the FDA's bioequivalence standards. The overwhelming majority of prescriptions written today are for the generic, at a small fraction of the brand price.
Can I drink alcohol with sildenafil?
A drink or two is generally not a problem. Heavier drinking both worsens erectile function on its own and adds to the blood-pressure-lowering effect of the medication, which can leave you dizzy or lightheaded.
Does sildenafil stop working over time?
The drug itself does not lose potency. If it stops working as well, that usually reflects progression of an underlying condition — cardiovascular disease, diabetes, or hormonal changes — which is worth investigating rather than simply escalating the dose.
Will sildenafil increase my sex drive?
No. It affects blood flow, not libido. If low desire is the primary issue rather than the mechanics of an erection, a PDE5 inhibitor is unlikely to help and you should raise that with a clinician.
Sources
- 1.Viagra (sildenafil citrate) prescribing information — U.S. Food and Drug Administration
- 2.Erectile Dysfunction: AUA Guideline — American Urological Association
- 3.Tainted sexual enhancement products — U.S. Food and Drug Administration