Strength & Format Selection

Sildenafil 20mg Tablets: Why the Low-Dose Pill Shows Up for ED

It's the same molecule as Viagra in a smaller tablet, approved for a different condition. Here's why it ends up on ED prescriptions and what that changes.

Explainer · 6 min read · Published October 18, 2026

Our starting-strength guide covers the three tablet sizes most people associate with sildenafil: 25, 50 and 100 mg. There's a fourth strength that keeps appearing in ED conversations, on discount-card search results and in telehealth plans: the 20 mg tablet. It's real, it's the same active ingredient, and it exists for a different reason entirely.

Where the 20 mg Tablet Comes From

Sildenafil was approved twice in the U.S., for two different conditions. As Viagra, it's approved for erectile dysfunction. As Revatio, it's approved for pulmonary arterial hypertension (WHO Group I), a serious lung-vessel condition, to improve exercise ability and delay clinical worsening.

Generic versions of both exist. That's why a pharmacy can stock generic sildenafil 20 mg tablets (the PAH strength) right next to generic 25, 50 and 100 mg tablets (the ED strengths). Chemically, it's the same drug. What differs is the approved use, the tablet size and the way each is typically priced.

Why It Shows Up on ED Prescriptions

Prescribers can, and some do, write the 20 mg tablet for ED. The arithmetic is simple: two tablets make 40 mg, three make 60 mg, five make 100 mg. Using a PAH-strength tablet for ED is off-label use, which is legal for a licensed prescriber and common across medicine, but it means the instructions come from the prescriber, not from the ED label.

The reasons people and prescribers choose it tend to be practical:

• Price at the counter. In many U.S. retail pharmacies, generic 20 mg tablets have been priced low per tablet, sometimes low enough that several of them cost less than one ED-strength tablet. Whether that's true where you fill depends on the pharmacy and any discount program; see our discount card explainer.
• Finer dose steps. Whole 20 mg tablets allow 20 mg increments without cutting anything, which avoids the accuracy problems covered in our tablet-splitting guide.
• Telehealth plans. Some online services sell ED sildenafil in 20 mg tablets for the same reasons.

How It Changes the Price Math

The right comparison is cost per dose, not cost per tablet. A 20 mg tablet that costs a fraction of a 100 mg tablet still has to be multiplied by the number of tablets your prescription says to take each time.

1. Find the per-tablet price for the 20 mg product (pack total divided by tablet count).
2. Multiply by the number of tablets per dose on your prescription.
3. Compare that against the per-dose price of a single 25, 50 or 100 mg tablet at the same pharmacy.
4. Factor in how many doses a month you'll realistically take. A quantity limit or a monthly fill cap can matter more than the per-tablet number.

Higher-dose regimens built from 20 mg tablets use a lot of tablets quickly, which can bump into pharmacy quantity rules or insurance limits. That's a practical reason some prescribers stick with one ED-strength tablet per dose.

Coverage: Why the PAH Label Doesn't Help an ED Claim

It's tempting to assume a drug that insurance covers for one condition is covered for another. For Medicare Part D, the federal exclusion is written around the use, not the molecule. The HHS Office of Inspector General explains that Part D excludes "a drug when used for the treatment of sexual or erectile dysfunction," effective January 1, 2007, while the same drug can still be a Part D drug when used for a different FDA-approved indication such as pulmonary hypertension.

In practice, a 20 mg sildenafil prescription written for PAH may be covered by a Part D plan, and the same tablet written for ED is not. Commercial plans set their own rules, and many require prior authorization or confirm the diagnosis for 20 mg sildenafil. Our Medicare explainer covers what Part D members do instead.

Who Should Be Most Careful

• Anyone already taking Revatio or another PAH sildenafil product. The Revatio label says: "Do not take VIAGRA or other PDE-5 inhibitors during treatment with REVATIO." Doubling up on the same drug class is dangerous.
• Anyone on nitrates for chest pain or heart disease. The Viagra label lists nitrate use as a contraindication because sildenafil potentiates their blood-pressure-lowering effect.
• People on alpha-blockers or multiple blood pressure medicines. Dose and timing need a clinician's input. Our safety and interactions guide has the full list.

Questions to Bring to the Prescriber

If 20 mg tablets come up as an option, a few questions make the conversation more useful:

• How many tablets per dose, and what's the maximum in a day? Get it written on the prescription so the pharmacist's label matches.
• How many tablets per fill? Higher-dose regimens built from small tablets use up a fill quickly, and some pharmacies or plans limit quantities.
• Is a single ED-strength tablet simpler for me? For someone who settles on 50 or 100 mg, one tablet may be easier to take correctly and to price-compare.
• Do any of my current medicines change the starting point? Alpha-blockers and some other drugs affect how sildenafil is started.

Whatever you decide, the dose that matters is the total milligrams per occasion, not the number printed on one tablet.

Frequently Asked Questions