Viagra and Cialis Dosage Guide: Strengths and How They're Prescribed

There's no single correct dose of Viagra or Cialis that applies to everyone. Both medications come in a range of strengths, and a licensed healthcare provider selects a starting point based on your health history, other medications, and how you respond over time. 

This guide covers what those strengths are and what generally goes into that decision, not a specific recommendation for you personally, since that's something only your provider can determine after reviewing your health information.

Viagra and Cialis Dosage: A Quick Overview

Sildenafil (Viagra) is available in three strengths: 25 mg, 50 mg, and 100 mg. Tadalafil (Cialis) comes in four strengths: 2.5 mg and 5 mg for daily use, and 10 mg and 20 mg for as-needed use. 

Your provider selects a starting strength based on your individual health profile, then adjusts it as needed based on how well it works for you and whether you experience any side effects.

Available Strengths of Viagra (Sildenafil)

Sildenafil's three strengths exist because response and tolerability vary from person to person. In fixed-dose clinical trials, 62% of patients on 25 mg reported improved erections, compared to 74% on 50 mg and 82% on 100 mg. [1] 

These findings show why a single standard dose was never going to work well for everyone. Some people get a strong response at lower doses, while others need higher doses to see the same benefit.

Higher isn't automatically better on an individual level. More of the active ingredient also means a higher chance of side effects like headache or flushing, which is why providers generally aim for the lowest strength that works well for a given person rather than defaulting to the highest one available.

Available Strengths of Cialis (Tadalafil)

Tadalafil (Cialis) is available in two distinct formats. The daily doses, 2.5 mg and 5 mg, are taken every day regardless of sexual activity, keeping a steady low level of the medication in your system. The as-needed doses, 10 mg and 20 mg, are taken before sexual activity, similar to how sildenafil is used. [2]

Which format makes sense depends heavily on lifestyle rather than any inherent advantage of one dose over another. Someone who's sexually active a couple of times a week might prefer the predictability of a daily low dose, while someone with less frequent or less predictable activity might prefer dosing only when needed. 

Our guide to how long Viagra and Cialis last covers how these formats compare in terms of duration.

How Your Provider Determines Your Starting Point

A handful of factors typically go into choosing a starting dose, beyond just picking a number.

• Age. Clearance of both medications tends to slow with age, which can influence the appropriate starting strength.
• Kidney and liver function. Since both drugs are processed through the liver and partly cleared by the kidneys, reduced function in either organ can change how a provider approaches dosing. [1]
• Other medications. Certain drugs can meaningfully change how much sildenafil or tadalafil ends up active in your bloodstream, covered in more detail below.
• Underlying health conditions. Cardiovascular health in particular plays a role, since both medications affect blood flow throughout the body, not just locally.
• Response and tolerability over time. If a starting dose doesn't work well or causes side effects that outweigh the benefit, your provider can adjust it going forward.

None of this is something to work out on your own. It's the entire reason a proper online consultation includes a detailed health questionnaire rather than just a menu of strengths to pick from.

Why Other Medications Matter for Dosing

Both sildenafil and tadalafil are broken down in the liver primarily by an enzyme called CYP3A4. Other medications that strongly affect this same enzyme can meaningfully change how much of the drug stays active in your system. [3]

Certain antifungal medications and some HIV medications, for example, can significantly increase how much sildenafil or tadalafil circulates in your body from a given dose, which is why product labelling for both medications includes specific dose limits when they're combined with these drugs. [1] [2] 

On the other hand, certain other medications can make either drug less effective by speeding up how quickly it's cleared. Grapefruit juice has a similar, if milder, effect on the same enzyme system.

None of this is something you're expected to track down yourself. Your provider asks about every medication and supplement you're taking, not just the ones that seem obviously related, to help you avoid drug interactions. This is the kind of detail a licensed healthcare provider, including those reviewing consultations through TreatMeNow, considers before your prescription is ever approved.

FAQ: Can I Split My Tablets to Adjust My Dose or Save Money?

It's a common question, especially once people notice that a higher-strength tablet often doesn't cost proportionally more than a lower one. The honest answer is that it depends on your specific prescription, and it's not a decision to make without checking first. 

Some tablets are manufactured with a score line for splitting, and some aren't. Taking a tablet that isn't designed to be split can affect how evenly the medication is distributed between halves.

There's also a difference between being prescribed a lower strength directly and splitting a higher one to approximate it. The two aren't always equivalent in practice, and your provider is best positioned to say whether splitting makes sense for your specific medication.

For more on how dosing ties into other parts of treatment, our full blog on erectile dysfunction covers cost, side effects, and duration in more depth.

If cost or dose adjustment is what's driving the question, here's a better way to approach it.

1. Ask your provider directly whether your specific prescription is designed to be split. Some are, some aren't, and it's a quick question to settle.
2. If cost is the real concern, say so directly. Our Viagra and Cialis pricing guides cover other ways to bring the cost down, including generic options that don't involve changing how you take your medication.
3. Don't assume a split tablet behaves the same as a lower-strength one prescribed directly. Bring this up with your provider rather than guessing.
4. If you're already splitting tablets on your own, mention it at your next check-in so your provider has an accurate picture of what you're taking.
5. Remember that dose changes in either direction are meant to be discussed with your provider rather than adjusted independently.