Generic Cialis (Tadalafil): Daily vs As-Needed, Compared on the Label's Own Numbers
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Generic Cialis Guide: Complete Information on Tadalafil Treatment - pharmacy guide
Generic Cialis is tadalafil. The brand belongs to Lilly, the molecule is now made by many manufacturers, and tablets sold as Vidalista, Tadalista or plain generic tadalafil contain the same active ingredient at the same strengths.
The interesting question is not brand against generic. It is that tadalafil is the only erection tablet with two licensed ways of taking it: a dose before sex, or a small dose every day. The FDA label reports side effects separately for each, and the two sets of numbers are not what most people expect. This guide puts them side by side.
The short answer
Tadalafil is a PDE5 inhibitor for erectile dysfunction. Taken as needed, the usual starting dose is 10 mg before sex, adjustable between 5 mg and 20 mg. Taken daily, the dose is 2.5 mg or 5 mg and you stop timing anything. Its half-life is 17.5 hours, far longer than sildenafil's four, and food does not affect it. In a trial that timed attempts a day and a half after one 20 mg dose, 64% of men succeeded against 37% on placebo. Side effects rise with dose on the as-needed schedule, while 5 mg daily adds far less headache and indigestion than 20 mg does. Nitrates are an absolute contraindication.
What generic Cialis is
Cialis was approved in the United States in 2003. Tadalafil is the active ingredient, and generic versions became available once the patent expired.
| Name | Who makes it | Strengths |
|---|---|---|
| Cialis | Lilly (brand) | 2.5, 5, 10, 20 mg |
| Generic tadalafil | Many manufacturers | 2.5, 5, 10, 20 mg |
| Vidalista | Centurion Laboratories, India | 2.5 to 60 mg |
| Tadalista | Fortune Healthcare, India | 5 to 60 mg |
| Adcirca | Same molecule, licensed for pulmonary hypertension | 20 mg |
Adcirca is worth knowing about for the same reason Revatio is with sildenafil: it is tadalafil under another name, and taking both means taking a double dose of one drug.
You will also see strengths above 20 mg sold online. Those sit outside what the label covers, and we deal with them in the high dose tadalafil guide.
How tadalafil works
Sexual stimulation releases nitric oxide in the penis. That raises cyclic GMP, which relaxes smooth muscle and lets blood in. PDE5 breaks cyclic GMP down. Tadalafil blocks PDE5, so the erection holds.
Like every drug in the class, it needs arousal to do anything. The difference from sildenafil is how long the drug stays in the body, and how selective it is. The label reports tadalafil as 700 times more potent at PDE5 than at PDE6, the retinal enzyme behind the blue tinge some men see on sildenafil. Sildenafil's margin at PDE6 is only about tenfold.
Why the 17.5 hour half-life changes the planning
Three numbers from the label explain tadalafil's reputation.
| Property | Tadalafil | What it means in practice |
|---|---|---|
| Terminal half-life | 17.5 hours | Roughly four times sildenafil's, which is why the window is measured in days rather than hours |
| Time to peak | Median 2 hours, range 30 minutes to 6 hours | Slower to arrive than sildenafil; the label says take it at least 30 minutes before, but that is the fast end |
| Food effect | None on rate or extent of absorption | A heavy meal does not weaken or delay it |
The slow peak is the part that gets missed. If sildenafil worked for you at one hour and you take tadalafil on the same schedule, you may be testing it before it has arrived.
The 36 hour window, tested directly
The label states that tadalafil taken as needed improved erectile function compared with placebo up to 36 hours after dosing. That is not an extrapolation from the half-life. Two studies timed intercourse attempts deliberately late.
In the first, 348 men were randomised to placebo or 20 mg, and asked to make attempts at about 24 hours and again at about 36 hours after a dose.
| Timing of attempt | Placebo | Tadalafil 20 mg |
|---|---|---|
| 22 to 26 hours after the dose | 37% (53 of 144) | 61% (84 of 138) |
| 33 to 39 hours after the dose | 37% (49 of 133) | 64% (88 of 137) |
The figure is the share of men reporting at least one successful intercourse in that window.
The second study, 483 men, measured the share of attempts that succeeded rather than the share of men. At 24 hours it was 42% on placebo, 56% on 10 mg and 67% on 20 mg. At 36 hours it was 33%, 56% and 62%.
Read together, the two studies show the effect is still clearly present a day and a half later. That is the licensed basis for the weekend nickname.
How well it works
The label reports the share of attempts in which the erection lasted long enough for successful intercourse, at the end of each study. Here are the two main US trials of 20 mg as needed alongside the two main trials of 5 mg daily.
| Trial | Placebo | Tadalafil |
|---|---|---|
| Study A, 20 mg as needed (placebo n=49, tadalafil n=146) | 25% | 50% |
| Study B, 20 mg as needed (n=48, n=159) | 23% | 64% |
| Study H, 5 mg daily, 24 weeks (n=94, n=97) | 31% | 57% |
| Study I, 5 mg daily, 12 weeks (n=54, n=109) | 37% | 67% |
Two things are worth reading off that table. Both schedules work: every trial roughly doubled the placebo success rate or did better. And the results for the same dose varied a lot between trials, 50% in Study A against 64% in Study B, which is a reminder that a single quoted percentage is narrower than it looks.
In Study H, 2.5 mg daily reached 50% against 57% for 5 mg, which is why 2.5 mg is the labelled starting dose for daily use and 5 mg the step up.
Side effects taken as needed
These are the reactions reported by at least 2% of men and more often than placebo across eight 12 week trials.
| Side effect | Placebo (N=476) | 5 mg (N=151) | 10 mg (N=394) | 20 mg (N=635) |
|---|---|---|---|---|
| Headache | 5% | 11% | 11% | 15% |
| Indigestion | 1% | 4% | 8% | 10% |
| Back pain | 3% | 3% | 5% | 6% |
| Muscle pain | 1% | 1% | 4% | 3% |
| Nasal congestion | 1% | 2% | 3% | 3% |
| Flushing | 1% | 2% | 3% | 3% |
| Pain in limb | 1% | 1% | 3% | 3% |
Headache and indigestion are the two that climb most clearly with dose. Indigestion goes from 4% at 5 mg to 10% at 20 mg.
Side effects taken daily
These are the reactions reported by at least 2% of men and more often than placebo across three 12 week trials of daily dosing. The label lists more rows than this; these are the ones that also appear on the as-needed table or reach 3%.
| Side effect | Placebo (N=248) | 2.5 mg daily (N=196) | 5 mg daily (N=304) |
|---|---|---|---|
| Headache | 5% | 3% | 6% |
| Indigestion | 2% | 3% | 5% |
| Nasopharyngitis | 4% | 4% | 3% |
| Back pain | 1% | 3% | 3% |
| Upper respiratory infection | 1% | 3% | 3% |
| Flushing | 1% | 1% | 3% |
| Muscle pain | 1% | 2% | 2% |
| Nasal congestion | 0% | 2% | 2% |
They stay close to placebo. Headache on 5 mg daily was 6% against 5% on a dummy tablet.
Reading those two tables together
Because the two schedules were tested in separate trial programmes with their own placebo groups, the fair comparison is how far each one sits above its own placebo.
| Side effect | 20 mg as needed, above placebo | 5 mg daily, above placebo |
|---|---|---|
| Headache | +10 points (15% vs 5%) | +1 point (6% vs 5%) |
| Indigestion | +9 points (10% vs 1%) | +3 points (5% vs 2%) |
| Back pain | +3 points (6% vs 3%) | +2 points (3% vs 1%) |
| Flushing | +2 points (3% vs 1%) | +2 points (3% vs 1%) |
| Muscle pain | +2 points (3% vs 1%) | +1 point (2% vs 1%) |
Headache and indigestion are where the difference lives. A 20 mg tablet produces a peak concentration around four times that of 5 mg, and those side effects track the peak. Daily dosing trades the peak for a steady low level. Back pain, flushing and muscle pain barely differ.
One number cuts the other way, and it belongs in the picture. In the daily trials 4.1% of men stopped because of side effects, against 2.8% on placebo. In the as-needed trials it was 3.1% against 1.4%. The excess over placebo is similar, 1.3 points against 1.7, and the daily figure includes one trial that ran for 24 weeks. So daily dosing produces fewer of the common complaints, but it is not a way to avoid side effects altogether.
Which schedule suits you
The label licenses both, so this is a preference rather than a medical ranking.
| As needed | Once daily | |
|---|---|---|
| Dose | 10 mg to start, range 5 to 20 mg | 2.5 mg to start, up to 5 mg |
| Timing | At least 30 minutes before, allowing for a median 2 hour peak | About the same time each day, no timing around sex |
| Suits | Sex once or twice a week | Sex more often, or wanting spontaneity |
| Headache and indigestion | Higher, rising with dose | Close to placebo at 5 mg |
| Drawback | Requires some planning | A tablet on days you do not need it |
Switching schedules is a conversation with a prescriber rather than something to do on your own, because the dose changes and the kidney and liver adjustments differ between the two.
Dose adjustments
Tadalafil's long half-life means impaired clearance matters more than it does with a short-acting drug. In clinical pharmacology studies, tadalafil exposure doubled in men with mild or moderate kidney impairment. The label's adjustments are specific to each schedule.
| Situation | As needed | Once daily |
|---|---|---|
| Mild kidney impairment (creatinine clearance 51 to 80 mL/min) | No adjustment | No adjustment |
| Moderate kidney impairment (31 to 50 mL/min) | Start at 5 mg, no more than once a day; maximum 10 mg, no more than once every 48 hours | No adjustment |
| Severe kidney impairment (under 30 mL/min) or dialysis | Maximum 5 mg, no more than once every 72 hours | Not recommended |
| Mild or moderate liver impairment (Child-Pugh A or B) | Do not exceed 10 mg once a day | Not extensively studied; use with caution |
| Severe liver impairment (Child-Pugh C) | Not recommended | Not recommended |
| Potent CYP3A4 inhibitor, such as ketoconazole or ritonavir | Maximum 10 mg, no more than once every 72 hours | Do not exceed 2.5 mg |
| Age over 65 | No adjustment | No adjustment |
Note the 48 and 72 hour intervals. With sildenafil the usual advice is a lower starting dose; with tadalafil it is a lower dose taken less often, because the drug is still present days later.
Nitrates: the absolute rule
Tadalafil is contraindicated with organic nitrates in any form. That covers nitroglycerin, isosorbide mononitrate and dinitrate, and recreational nitrites. The other contraindication is a serious hypersensitivity reaction to tadalafil, whether taken as Cialis or as Adcirca.
The label gives a specific window for emergencies. If a nitrate is medically necessary in a life-threatening situation after someone has taken tadalafil, at least 48 hours should pass after the last dose before a nitrate is considered, and even then only under close medical supervision. That window follows from the long half-life. If you are ever treated for chest pain, say when you last took tadalafil and at what dose.
Alpha blockers
Alpha blockers for prostate symptoms are vasodilators, and so is tadalafil, so the blood pressure effects add up. The label's advice is sequencing: be stable on the alpha blocker first, then start tadalafil at the lowest recommended dose.
Alcohol
Both alcohol and tadalafil are mild vasodilators. The label warns that substantial drinking, which it defines as 5 units or more, combined with tadalafil can increase the chance of a faster heart rate, a drop in blood pressure on standing, dizziness and headache. A drink or two is a different matter from a heavy night, and alcohol works against erections on its own regardless.
Back pain and muscle ache
Back pain and muscle pain sit higher on tadalafil's table than on sildenafil's, and this is the side effect men most often ask about.
On the label numbers, back pain ran at 6% on 20 mg as needed against 3% on placebo, and muscle pain at 3% to 4% against 1%. The label describes it as diffuse aching in the lower back, buttocks or thighs that generally appeared 12 to 24 hours after the dose and typically resolved within 48 hours, mostly mild or moderate and without treatment. On the daily schedule, back pain was reported by 3% of men, though that programme's placebo rate was also lower.
Side effects that need urgent attention
The class warnings apply to tadalafil as they do to every PDE5 inhibitor.
An erection lasting more than four hours. Seek help immediately; untreated priapism can cause permanent damage.
Sudden vision loss in one or both eyes, which can signal non-arteritic anterior ischemic optic neuropathy.
Sudden hearing loss, sometimes with ringing or dizziness.
Chest pain, dizziness or nausea beginning during sex is a reason to stop and speak to a doctor.
Tadalafil against sildenafil
These two account for most ED prescriptions, and they differ more in handling than in effectiveness.
| Tadalafil | Sildenafil | |
|---|---|---|
| Half-life | 17.5 hours | About 4 hours |
| Time to peak | Median 2 hours | Median 1 hour |
| Window of effect | Tested up to 36 hours | Strongest in first 2 hours |
| High fat meal | No effect | Peak about an hour later and 29% lower |
| Licensed daily option | Yes | No |
| Selectivity over retinal PDE6 | 700-fold | About 10-fold |
| Headache at top as-needed dose | 15% | 28% |
| Back pain at top as-needed dose | 6% | 4% |
Read across and the trade is legible. Tadalafil is easier to plan around and less likely to affect colour vision; sildenafil arrives faster. The headache and back pain figures come from separate trial programmes, so read them as a direction rather than a head to head result. Our tadalafil versus sildenafil comparison uses a meta-analysis of head to head trials, and the sildenafil guide covers the other side.
Generic tadalafil against brand Cialis
A generic must contain the same active ingredient at the same strength and deliver comparable blood levels to be approved. Inactive ingredients, tablet appearance and the manufacturer differ.
What matters is whether the plant that made it has been inspected. A WHO-GMP certified facility has been assessed against a recognised standard; an unnamed supplier has not. Our guide to what WHO-GMP certification means explains what that covers. The Vidalista 20 mg versus Cialis comparison sets one Indian generic against the brand, including what is and is not known about its bioequivalence, and the Vidalista 20 mg guide covers that product in detail.
Buying tadalafil online
Tadalafil is prescription-only in the United States, the UK, Australia and most markets. Before ordering, check that the manufacturer is named and verifiable, that the strength is stated in milligrams of tadalafil, that the seller does not claim you need no prescription, and that there is a real address and a way to reach someone.
Treat herbal erection supplements with suspicion. The FDA regularly finds undeclared tadalafil or sildenafil in them, which means an unknown dose with no nitrate warning. Our guide to checking whether an online pharmacy is legitimate covers verification.
When tadalafil looks like it failed
- Judged too early. Median time to peak is two hours, not thirty minutes.
- No sexual stimulation. The drug does nothing on its own.
- One attempt only. The trials ran for 12 weeks or longer.
- Dose too low. 10 mg is a starting dose, and the range runs to 20 mg.
- Alcohol. It works against erections regardless of the tablet.
Our ED medicine dosage guide covers adjustment across the class, and the avanafil guide covers the fastest option if timing is the problem.
When to see a doctor
Before starting: if you have heart disease, a heart attack or stroke in the last six months, very low or uncontrolled high blood pressure, kidney or liver impairment, or take nitrates or an alpha blocker.
After starting: if 20 mg used properly on several occasions does not work, if side effects persist, or if you have an erection lasting over four hours, sudden vision loss or sudden hearing loss.
Erectile dysfunction is frequently the first visible sign of cardiovascular disease or undiagnosed diabetes. A tablet that works does not answer that question, which is the best reason to raise it with a doctor rather than self-treating. Our erectile dysfunction guide covers the underlying causes.
For every Tadalista strength and type set against the same label data, see our Tadalista strengths and types comparison.
Sources
- CIALIS (tadalafil) tablets, US prescribing information, sections 2, 4, 5, 6.1, 7, 8, 12 and 14. DailyMed
- As-needed adverse reactions: section 6.1, Table 1, eight 12 week trials (placebo N=476, 5 mg N=151, 10 mg N=394, 20 mg N=635).
- Once-daily adverse reactions: section 6.1, Table 2, three 12 week trials (placebo N=248, 2.5 mg N=196, 5 mg N=304).
- 24 and 36 hour studies: section 14. Efficacy by schedule: section 14, Tables 10 and 16.
- Sildenafil comparison figures: VIAGRA (sildenafil citrate) US prescribing information, sections 6.1, 12.1 and 12.3.
This article is for information only and is not medical advice. Tadalafil is a prescription medicine. Talk to a doctor or pharmacist before starting, stopping or changing any treatment.
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