Which one starts working faster?

Both labels state timing in their dosing sections, and those figures are in the table above. Avanafil is the one in this class specifically developed for a shorter onset.

Both are off patent and both are cheap as generics. Price differences between them at a pharmacy come from pack size and local supply, not from the substance.

Can they be alternated?

That is a prescribing question rather than a label question. Neither document describes switching between them, so this page does not advise on it.

Comparison

Sildenafil and tadalafil, compared from both labels

The most common question in this category, and the labels answer most of it. One difference is real and practical, one is a matter of price, and the rest is closer to marketing than to medicine.

From the approved label

The two labels, side by side

	Viagra	Cialis
Approved uses	ViagraVIAGRA is a phosphodiesterase-5 (PDE5) inhibitor indicated for the treatment of erectile dysfunction (ED)	CialisCIALIS ® is a phosphodiesterase 5 (PDE5) inhibitor indicated for the treatment of: erectile dysfunction (ED) the signs and symptoms of benign prostatic hyperplasia (BPH)
Forms and strengths	ViagraVIAGRA is supplied as blue, rounded diamond shaped film-coated tablets containing sildenafil citrate equivalent to 25 mg, 50 mg, or 100 mg of sildenafil.; Tablets are debossed with "VIAGRA" on one side and "VGR 25", "VGR 50" or "VGR 100" on the other to indicate the dosage strengths.; Tablets: 25 mg, 50 mg, 100 mg	CialisThree strengths of almond-shaped tablets are available in different sizes and different shades of yellow: 5 mg tablets debossed with "C 5" 10 mg tablets debossed with "C 10" 20 mg tablets debossed...
How it is taken	ViagraBased on effectiveness and toleration, may increase to a maximum of 100 mg or decrease to 25 mg	CialisDo not split CIALIS tablets; entire dose should be taken. CIALIS for use as needed: ED: Starting dose: 10 mg as needed prior to sexual activity. Increase to 20 mg or decrease to 5 mg based upon efficacy/tolerability. Improves erectile function compared to placebo up to 36 hours post dose. Not to be taken more than once per day.
Must not be used when	ViagraAdministration of VIAGRA to patients using nitric oxide donors, such as organic nitrates or organic nitrites in any form. VIAGRA was shown to potentiate the hypotensive effect of nitrates; Known hypersensitivity to sildenafil or any component of tablet; Administration with guanylate cyclase (GC) stimulators, such as riociguat Nitrates Consistent with its known effects on the nitric oxide/cGMP pathway, VIAGRA was shown to potentiate the hypotensive effects of nitrates, and its administration to patients who are using nitric oxide donors such as organic nitrates or organic nitrites in any form either regularly and/or intermittently is therefore...	CialisAdministration of CIALIS to patients using any form of organic nitrate is contraindicated.; CIALIS was shown to potentiate the hypotensive effect of nitrates.; History of known serious hypersensitivity reaction to CIALIS or ADCIRCA ®.; Administration with guanylate cyclase (GC) stimulators, such as riociguat.
Common side effects	Viagramost common adverse reactions reported in clinical trials (≥ 2%) are headache, flushing, dyspepsia, abnormal vision, nasal congestion, back pain, myalgia, nausea, dizziness, and rash.; Most common adverse reactions (≥ 2%) include headache, flushing, dyspepsia, abnormal vision, nasal congestion, back pain, myalgia, nausea, dizziness and rash To report SUSPECTED ADVERSE REACTIONS, contact Viatris at 1-877-446-3679 (1-877-4-INFO-RX) or FDA at 1-800-FDA-1088 or www.	CialisMost common adverse reactions (≥2%) include headache, dyspepsia, back pain, myalgia, nasal congestion, flushing, and pain in limb.
Boxed warning	Viagra-	Cialis-
Label holder	ViagraViatris Specialty LLC	CialisEli Lilly and Company
Label version	Viagra17 November 2023	Cialis3 June 2026

Built at page render time from the same imported label data as the medicine pages, so it cannot drift away from them.

Written by us

The difference that is real

Duration. Tadalafil remains active in the body for far longer than sildenafil, and that single property is what produces every practical difference between them: whether a tablet has to be timed before sex, whether a daily low dose makes sense, and whether food matters much.

The second real difference is scope of approval. Tadalafil holds an approval for an enlarged prostate as well, including for both conditions together. Sildenafil holds a second approval too, but for pulmonary hypertension under a different brand name, which is a different medicine in practice at a different dose.

What the labels do not say

Neither label claims to work better than the other. Milligram figures cannot be compared across two substances, and a higher number on one box says nothing about strength relative to the other.

The contraindications are effectively shared. Both are contraindicated with nitrates, both interact with alpha blockers used for the prostate, and both carry the same class warnings. Anyone choosing between them on safety grounds is choosing between two documents that say much the same thing.

Questions

Which one starts working faster?: Both labels state timing in their dosing sections, and those figures are in the table above. Avanafil is the one in this class specifically developed for a shorter onset.
Is one cheaper?: Both are off patent and both are cheap as generics. Price differences between them at a pharmacy come from pack size and local supply, not from the substance.
Can they be alternated?: That is a prescribing question rather than a label question. Neither document describes switching between them, so this page does not advise on it.

Sources

Viagra: prescribing informationDailyMed, US National Library of Medicine. Label version 17 November 2023
Cialis: prescribing informationDailyMed, US National Library of Medicine. Label version 3 June 2026