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Sexual function

Tadalafil

The longest-acting PDE-5 inhibitor (known as Cialis). Up to a 36-hour window, on demand or low daily.

2 min read 5 sources

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Still from the explainer video about this entry
Compound approved · since 2002 according to ChEMBLLab tested in the shop

No time to read it all? The video sums up the whole entry in about a minute, from how it works to the studies and storage.

Summary

At a glance

Sources checked on 26 Oct 2026

Window in trials
36 hours

59.2% successful attempts after 36 hours, 28.3% on placebo3

Improved erections
81 %

highest study dose after 12 weeks, 35% on placebo1

Erectile function (IIEF-EF)
+7.9 points

change from baseline, highest study dose, 5 trials with 1,112 men1

Daily use tested
1,913 men

6 trials over 12 weeks, two low levels versus placebo2

Severe ED: clinically important improvement
44.5 %

higher daily level, 11.6% on placebo2

  • Tadalafil inhibits the enzyme PDE5. ChEMBL lists PDE5A as its target, just as for sildenafil.5
  • In five trials with 1,112 men 81 percent reported improved erections on the highest study dose, 35 percent on placebo.1
  • A dedicated trial tested attempts 24 and 36 hours after intake. After 36 hours 59.2 percent were successful, 28.3 percent on placebo.3
  • Daily use at two low levels also improved erectile function in six trials with 1,913 men.2
  • Tadalafil is an approved compound. Everything here is the state of research, not a recommendation.5
Profile

Updated May 2026

How long does it stay in the body?

Share left after one dose, calculated with a half-life of ~17.5 hours

Half-life ~17.5 hours
After 35 hours: 25 %
Hour 18 · 49 %Hour 35 · 25 %Hour 53 · 12.3 %Hour 88 · 3.1 %

Simplified model without an absorption phase, half-life from the TPD lexicon.

Class
PDE-5 inhibitor

also Cialis

Route
Oral

on demand or daily

Duration
Up to ~36 hours
Half-life
~17.5 hours
Sizes
5 to 20 mg

3 sizes in the shop

Contents 15 sections
  1. At a glance
  2. Titration
  3. What is Tadalafil?
  4. How it works
  5. How to take it
  6. Tadalafil vs Sildenafil
  7. What the research shows
  8. Research status
  9. Side effects
  10. Safety and interactions
  11. Storage
  12. Related compounds
  13. FAQ
  14. Glossary
  15. Sources

Getting started

Common doses

Either low daily (continuous) or on demand. At most once a day.

Dosing. Loading the dosing information …

What is Tadalafil?

Tadalafil is the longest-acting PDE-5 inhibitor and known under the brand name Cialis. Like sildenafil it is used for erectile function; the big difference is duration: a single window lasts up to 36 hours.

Hence the nickname "weekend pill": you do not have to time dosing tightly to the moment. Tadalafil can be taken on demand or as a low daily dose.

How it works

The mechanism is the same as sildenafil: tadalafil blocks the enzyme PDE-5, so the vessel-relaxing messenger in the penis lasts longer and the erection comes more easily. Here too: it amplifies the natural response but does not replace arousal.

The key is the long half-life of about 17.5 hours. That gives the broad window and the option to dose tadalafil low daily, so it is simply "there" continuously.

Where it acts

Where tadalafil acted in studies

Tap a point or a card. Colour = PDE5, grey = observed in studies.

  1. Erectile tissue

    Erectile function (IIEF-EF) up 7.9 points on average at the highest study dose1

    PDE5
  2. Blood vessels

    Effect still measurable 36 hours after intake3

    PDE5
  3. Stomach

    Indigestion more common than on placebo3

    Observed in trials
  4. Muscles

    Muscle pain more common than on placebo3

    Observed in trials

Targets in the ChEMBL database5

Compound CHEMBL779: one recorded mechanism, Inhibitor.

Phosphodiesterase 5A
Gene
PDE5A
UniProt
O76074
ChEMBL
CHEMBL1827
Action
Inhibitor
Glassy honeycomb-like tissue with light blue chambers holding blue molecules
Tadalafil inhibits PDE5, the vessel-relaxing messenger stays active for longer. Symbolic image.

How to take it

Two ways are common:

  • On demand: 10 or 20mg as needed. Thanks to the long window you do not have to time it tightly.
  • Daily: 2.5 or 5mg every day. Then you are covered continuously, without thinking about dosing before the moment.

Tadalafil is less sensitive to fatty food than sildenafil. At most once a day.

White tablet bottle with a black TPD label for tadalafil, next to it a small white box, four tablets and a glass of water
Tablet on demand or daily at a low level, at most once a day. Symbolic image.

Tadalafil vs Sildenafil

The most common question in this area. The difference is mainly timing:

  • Tadalafil lasts up to 36 hours, can be dosed low daily and is more robust against food. Ideal for spontaneity.
  • Sildenafil lasts about 4 to 6 hours, fast onset, classically taken shortly before, but reacts more sensitively to fatty food.

In short: tadalafil for a long, relaxed window, sildenafil for the single, planned occasion. Both work through the same mechanism.

Comparison

Four PDE5 inhibitors in the lexicon

All four inhibit the same enzyme. The differences lie in duration and intake. Tap a card to open its entry.

PDE5 inhibitor, approved 2002 Tadalafil PDE5
PDE5 inhibitor, approved 1998 Sildenafil PDE5 PDE5 inhibitor, approved 2003 Vardenafil (Levitra) PDE5 PDE5 inhibitor, approved 2011 Avanafil (Stendra, Spedra) PDE5

According to ChEMBL: all four inhibit PDE5A, first approval sildenafil 1998, tadalafil 2002, vardenafil 2003, avanafil 2011. 5

What the research shows

Tadalafil is very solidly evidenced. An integrated analysis of five controlled studies (Brock, 2002) showed clear improvements in erectile function and documented the response window of up to 36 hours. A later analysis (Porst, 2014) additionally confirmed the efficacy of the low daily dose (2.5 and 5mg).

The studies with links are in the source block below.

Study results

What the trials measured

Interactive: switch tabs, tap points, show or hide arms. Arms are named relative to each other, no dosing advice.

Successful attempts after intake3

Share of successful attempts in percent, 348 men, 4 weeks per time point

After about 24 hours3
Placebo 29.1%
Tadalafil 20 mg (highest study dose) 52.9%
After about 36 hours3
Placebo 28.3%
Tadalafil 20 mg (highest study dose) 59.2%

Values from the abstract. Successful meant intercourse to ejaculation according to the diary. 327 of 348 men completed the trial.

Result after 12 weeks1

Integrated analysis of 5 trials with 1,112 men, intake on demand

Improved erections at the end1 Global assessment question
Placebo 35%
Tadalafil 20 mg (highest study dose) 81%
Attempts completed successfully1 Diary question 3, no placebo value in the abstract
Tadalafil 20 mg (highest study dose) 75%

Values from the abstract. The erectile function score (IIEF-EF) rose by 7.9 points on average at the highest study dose. The effect was similar across age, severity and causes.

Clinically important improvement2

Share of men in percent, 6 trials with 1,913 men over 12 weeks

Mild ED2
Daily, lower level 54.3%
Daily, higher level 74.8%
Moderate ED2
Daily, lower level 51.3%
Daily, higher level 63.1%
Severe ED2 only here with a placebo value in the abstract
Placebo 11.6%
Daily, lower level 33.7%
Daily, higher level 44.5%

Values from the abstract, a purely descriptive analysis of pooled data. For mild and moderate ED the abstract gives no placebo value.

Successful intercourse versus placebo2

More successful attempts (diary question 3) than on placebo, in percentage points

Difference to placebo2
Daily, lower level 17.8 pp
Daily, higher level 23.6 pp

Values from the abstract (LS means). The IIEF-EF score was 4.2 and 5.4 points above placebo.

Glass lab cabinet with petri dishes, in the middle a frosted glass model and an hourglass
Trials on the response window and daily intake. Symbolic image.

Research status

Where the research stands

Tadalafil has been approved since 2002. On ClinicalTrials.gov 291 trials list tadalafil among their interventions, also on the prostate and pulmonary hypertension. Shown are registered phase 3 trials on erectile function and two from other uses. As of 26 Oct 2026. 4

  1. Preclinical Basis: inhibition of PDE5
  2. Phase 1 no registered trial
  3. Phase 2 no registered trial
  4. Phase 3 6 trials, 6 completed
  5. Approval since 2002 according to ChEMBL
2,897 participants in phase 3 Approved: ChEMBL lists tadalafil with phase 4 as the highest phase and first approval in 2002.5
Show all 6 phase 3 trials on a timelineHide timeline 6 completed 0 running 0 with results
Phase 3

Bar: start to primary endpoint (planned for running trials). Green = completed, blue = progress until 26 Oct 2026.

Side effects

The most common effects are mild: headache, indigestion (dyspepsia), facial flush, stuffy nose. Typical for tadalafil are occasional back or muscle aches that usually pass after a day or two. All dose-dependent.

Safety and interactions

As with all PDE-5 inhibitors, the most important point: never combine with nitrates. That covers heart nitrates (e.g. nitroglycerin) and "poppers" (amyl nitrite). The combination can crash blood pressure dangerously. Because tadalafil acts for so long, that risk exists over an especially long window.

Caution also with alpha-blockers and existing cardiovascular disease. With pre-existing conditions or other medication, clear it with a doctor first.

Storage

Store the tablets dry, at room temperature and protected from light, out of reach of children. Keep the original packaging closed and mind the expiry date.

Three white capsule bottles on a bright shelf next to a folded light blue towel
Store dry, at room temperature and protected from light. Symbolic image.

Related

Related compounds

Same targets or blends with Tadalafil: all in the TPD lexicon.

Tadalafil
Sildenafil Same enzyme, shorter duration Vardenafil (Levitra) Same enzyme Avanafil (Stendra, Spedra) Same enzyme Sildenafil + Tadalafil (combo) Contains tadalafil Kamagra Oral Jelly (Sildenafil) Sildenafil as a jelly

FAQ

Common questions about Tadalafil

Short answers, each backed by the sources below.

Is tadalafil approved?

Yes. ChEMBL lists tadalafil with phase 4 as the highest phase and first approval in 2002. ClinicalTrials.gov lists 291 trials with tadalafil, as of 26 October 2026.54

How long does tadalafil work according to trials?

In a trial with 348 men attempts were scheduled about 24 or 36 hours after intake. After 24 hours 52.9 percent were successful, after 36 hours 59.2 percent. On placebo it was 29.1 and 28.3 percent.3

What do the trials on intake on demand show?

An integrated analysis of five trials with 1,112 men found an improvement of 7.9 points in the IIEF-EF score at the highest study dose. 81 percent reported improved erections, 35 percent on placebo. The effect was similar across age and causes.1

Was daily intake studied?

Yes. Six trials with 1,913 men tested two low daily levels over 12 weeks. Both improved erectile function versus placebo. In severe ED 44.5 percent reached a clinically important improvement at the higher level, 11.6 percent on placebo.2

Which side effects occurred in the trials?

Headache and indigestion were most common. In the 36-hour trial headache, flushing, indigestion and muscle pain occurred more often than on placebo. The trials on daily intake showed no unexpected safety findings.132

How does tadalafil differ from sildenafil?

According to ChEMBL both inhibit the same enzyme PDE5A. For tadalafil trials document a window of up to 36 hours. A registered comparison tested daily intake against a PDE5 inhibitor on demand.534

Glossary

Terms explained briefly

Dotted words in the text open these explanations directly.

Alpha blocker
Drugs for high blood pressure or prostate symptoms that also lower blood pressure.
Dyspepsia
Indigestion such as fullness or heartburn.
Half-life
Time until half of a compound in the blood has been cleared.
IIEF-EF
Questionnaire score for erectile function. A rise of about 4 points is considered clinically important.
Integrated analysis
Joint analysis of the data of several trials by one sponsor.
Nitrates
Vessel-widening drugs, for example for chest pain. Together with PDE5 inhibitors blood pressure can drop sharply.
On demand
Intake when needed before an occasion instead of every day.
PDE5 inhibitor
Compound that slows the enzyme phosphodiesterase 5. A vessel-relaxing messenger then stays active for longer.
Placebo
Dummy preparation without active substance. Comparing against it shows what is due to the substance itself.
Poppers
Inhaled nitrites such as amyl nitrite. They act on the vessels like nitrates.

Evidence

Sources

Show all 5 sourcesHide sources 3 Studies1 Trial registry1 Database checked 26 Oct 2026

Studies

  1. Integrated analysis of 5 trials on efficacy and safety

    Brock et al., Journal of Urology, 2002

    DOI 10.1016/S0022-5347(05)64442-4 PMID 12352386
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  2. Daily intake: integrated analysis of 6 trials with 1,913 men

    Porst et al., European Urology, 2014

    DOI 10.1016/j.eururo.2013.09.037 PMID 24119319
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  3. Effect 24 and 36 hours after intake

    Porst et al., Urology, 2003

    DOI 10.1016/s0090-4295(03)00359-5 PMID 12837435
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed

Trial registry

  1. All trials with tadalafil on ClinicalTrials.gov

    ClinicalTrials.gov, U.S. National Library of Medicine

    Checked 26 Oct 2026 via ClinicalTrials.gov API v2

Database

  1. Tadalafil and other PDE5 inhibitors in ChEMBL (target and approval)

    ChEMBL, EMBL-EBI (CHEMBL779, CHEMBL1737, CHEMBL1339, CHEMBL1963681)

    Checked 26 Oct 2026 via ChEMBL

In the shop

Tadalafil in the catalog

Sizes, prices and shipping times are on the product page.

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