Men’s health › Sildenafil vs tadalafil
BalanzGM is reader-supported — we may earn a commission from links on this site, at no extra cost to you. See our affiliate disclosure. This article is information, not medical advice.
The short version. Same mechanism, very different pharmacology. Sildenafil is short and sharp — peak within an hour, half-life about four hours, and a visual side effect that climbs steeply with dose. Tadalafil lasts around 17.5 hours, can be taken as a low daily dose so timing disappears as a consideration, is also approved for benign prostatic hyperplasia, and trades the visual effect for back pain and muscle ache. Neither is “stronger”. They are different tools.
The mechanism they share
Both are phosphodiesterase type 5 inhibitors. From the Cialis label: “The inhibition of phosphodiesterase type 5 (PDE5) enhances erectile function by increasing the amount of cGMP.” The Viagra label puts it the same way — sildenafil “enhances the effect of NO by inhibiting phosphodiesterase type 5 (PDE5), which is responsible for degradation of cGMP in the corpus cavernosum.”
Neither creates arousal. They remove the brake on a signal that arousal starts. No signal, no effect — which is why “it did not work” sometimes means the setting, not the drug.
Side by side, from the labels
| Sildenafil (Viagra) | Tadalafil (Cialis) | |
|---|---|---|
| Approved for | Erectile dysfunction | ED, the signs and symptoms of BPH, and both together |
| Timing | “approximately 1 hour before sexual activity”; may be taken “anywhere from 30 minutes to 4 hours before” | “10 mg, taken prior to anticipated sexual activity” — no fixed window given |
| Time to peak | 30 to 120 minutes, median 60 | 30 minutes to 6 hours, median 2 hours |
| Half-life | “about 4 hours” | “17.5 hours in healthy subjects” |
| Doses | 25 / 50 / 100 mg, as needed | 5 mg, 10 mg and 20 mg as needed; 2.5 or 5 mg once daily |
| Frequency | Once per day maximum | Once per day maximum |
| Food | With or without; a high-fat meal delays peak by about 60 minutes and cuts peak concentration 29% | “may be taken without regard to food” — no food effect described |
The daily option is the real structural difference
Tadalafil has a once-daily form that sildenafil does not. For ED: “2.5 mg, taken at approximately the same time every day, without regard to timing of sexual activity”, which may be increased to 5 mg. For BPH: 5 mg daily. For both conditions together: 5 mg daily.
What that changes is not potency but planning. Nothing has to be timed.
Two different side-effect profiles — and the reason is mechanistic
Neither drug is perfectly selective, and what each one cross-inhibits shapes what you feel.
Sildenafil: vision, and it is dose-dependent
From the Viagra label’s fixed-dose trials (25 / 50 / 100 mg vs placebo):
| Adverse reaction | 25 mg | 50 mg | 100 mg | Placebo |
|---|---|---|---|---|
| Headache | 16% | 21% | 28% | 7% |
| Flushing | 10% | 19% | 18% | 2% |
| Dyspepsia | 3% | 9% | 17% | 2% |
| Abnormal vision | 1% | 2% | 11% | 1% |
| Nasal congestion | 4% | 4% | 9% | 2% |
The label describes the visual effect as “mild to moderate in severity and transient, predominantly color tinge to vision, but also increased sensitivity to light, or blurred vision”, and attributes it to weaker cross-inhibition of PDE6 in the retina, with difficulty “discriminating blue/green” at higher doses. Note the jump from 1% at 25 mg to 11% at 100 mg. Dose matters.
Tadalafil: back and muscles, delayed
From the Cialis label, as-needed dosing (10–20 mg vs placebo): headache 11–15% vs 5%, dyspepsia 8–10% vs 1%, back pain 5–6% vs 3%, myalgia 3–4% vs 1%, nasal congestion 3% vs 1%, flushing 3% vs 1%.
The timing is characteristic: “back pain or myalgia generally occurred 12 to 24 hours after dosing and typically resolved within 48 hours.” This is attributed to cross-inhibition of PDE11. If you ache the next day, that is the recognised pattern, not something new.
Two other contrasts worth noting. Flushing is markedly lower with tadalafil — 3% against up to 19% for sildenafil. And on the once-daily 2.5–5 mg regimen, headache runs 3–6% against 5% on placebo, which is to say barely distinguishable.
The contraindications — identical, and not negotiable
Guanylate cyclase stimulators. “Do not use VIAGRA in patients who are using a GC stimulator, such as riociguat.” Same for Cialis.
Known hypersensitivity to the drug or its components.
Cardiovascular status — a question about sex, not only about the pill
The Viagra label: “There is a potential for cardiac risk of sexual activity in patients with preexisting cardiovascular disease. Therefore, treatments for erectile dysfunction, including VIAGRA, should not be generally used in men for whom sexual activity is inadvisable because of their underlying cardiovascular status.”
Both labels list groups excluded from their trials, so safety is simply unknown there: recent myocardial infarction or stroke, unstable angina, significant heart failure, uncontrolled arrhythmias, and blood pressure below 90/50 or poorly controlled hypertension. Viagra also notes retinitis pigmentosa.
Alpha-blockers
“Caution is advised when PDE5 inhibitors are co-administered with alpha-blockers.” Cialis adds that patients “should be stable on alpha-blocker therapy prior to initiating a PDE5 inhibitor”, starting at the lowest dose, and that combining Cialis with an alpha-blocker “is not recommended for the treatment of BPH.”
Stop and seek care
- Priapism. Viagra: an erection beyond 4 hours needs “immediate medical assistance. If priapism is not treated immediately, penile tissue damage and permanent loss of potency could result.”
- Sudden vision loss (NAION). Stop all PDE5 inhibitors and seek medical attention.
- Sudden hearing loss. Same instruction.
Which one
A clinician’s call, and it turns on practical things: whether you also have BPH symptoms, whether you would rather plan around a dose or not think about it, whether you are more bothered by flushing and colour tinge or by next-day back ache, and what else you take. Both are on the AUA’s strongly recommended list. Neither is a substitute for finding out why the ED is there — see causes and treatments.
Sources
- FDA prescribing information, VIAGRA (sildenafil citrate), rev. 08/2017 — accessdata.fda.gov
- FDA prescribing information, CIALIS (tadalafil), rev. 02/2018 — accessdata.fda.gov
- American Urological Association, “Erectile Dysfunction: AUA Guideline”, approved April 2018 — auanet.org
More in the men’s health hub: ED causes and treatments · online vs in-person care
Medical disclaimer. This article is for general information only and is not medical advice. It is not intended to diagnose, treat, cure or prevent any condition. Prescription treatments require evaluation by a US-licensed clinician, who decides whether treatment is appropriate for you. Talk to your own healthcare provider before starting, stopping or changing any medication. Never combine a PDE5 inhibitor with any nitrate. Individual results vary.
