If it lasts 36 hours, is that 36 hours of erection?
Ten tablets of 10 mg at four counters, and why halving a 20 mg tablet is not the saving it looks like
The rows below cover the on-demand strength at four licensed counters. Elysia Med is a reference and dispenses nothing.
| Pharmacy | Strength / count | How the window works | Official page |
|---|---|---|---|
| Walmart | 10 mg x 10 | Ordinary cash counter | Walmart pharmacy |
| Sam's Club | 10 mg x 10 | Club pharmacy; membership may apply | Sam's Club pharmacy |
| Meijer | 10 mg x 10 | Midwest grocery pharmacy counter | Meijer pharmacy |
| Cost Plus Drugs | 10 mg x 10 | Mail-order cash list | Cost Plus Drugs pharmacy |
Ten milligrams in a pack of ten is quoted below at Walmart, Sam's Club, Meijer and Cost Plus Drugs, because 10 mg is what a first on-demand prescription usually carries. Published figures for that count move with ZIP code and with the month, so treat any of them as a reason to telephone the counter. Brand Cialis still exists and still costs several times the generic; almost nothing dispensed in the United States now is brand.
Each row links to the pharmacy's own site. Coupon services publish separate figures for the same count and are named in the caption instead, because a coupon number and a shelf number describe different transactions.
The saving trick that circulates on price pages is to buy 20 mg tablets and cut them in half. The label closes that off in one line: do not split tadalafil tablets, the entire dose should be taken. The tablets are not scored, and a broken film coat gives an unreliable fraction where a clean 10 mg was intended. What genuinely moves the monthly figure is which route was prescribed, how many tablets that route uses, and which pharmacy fills it.
Every strength is prescription-only in the United States, telehealth included. The rest of the medicine list gets read before the strength is picked, and the nitrate rule is why that order matters.
Cardiac fitness is settled before the strength is chosen
The gate on this class is cardiac, and it is assessed before anyone discusses how firm the erections are.
Sex is exertion, roughly the work of two flights of stairs. A recent myocardial infarction, unstable angina, an uncontrolled arrhythmia, decompensated heart failure or blood pressure nobody has yet controlled are reasons to pause the whole discussion instead of adjusting a milligram figure. Vascular disease is also the commonest thing sitting underneath the original complaint, which why an erection fails goes into.
A heart attack last year does not close the door. Plenty of men are cleared after an uncomplicated recovery, and that judgement belongs to whoever manages the heart. What does close the door is a nitrate on the list, and a 17.5-hour half-life means no timing trick reopens it.
Dr Marc Vidal reviewed this page. What he asks men to bring to the appointment is the packets themselves, over-the-counter purchases included, and a straight answer about chest pain on exertion. His background is on the reviewer page.
Back and thigh ache that arrives a day after the tablet
The complaint that separates this drug from the short-acting two turns up a day later, which is why men blame the mattress, the gym or their kidneys for it.
| What happens | How often, and when | What to do about it |
|---|---|---|
| Headache, flushing, blocked nose, indigestion | Commonest effects; more frequent at 20 mg | Usually settles; simple analgesia |
| Back pain or myalgia | 5-6 percent; 12-24 hours after the dose | Clears within 48 hours; a fair reason to try another PDE5 drug |
| Erection past four hours | Rare | Emergency department the same hour |
| Sudden loss of vision or hearing | Rare, including NAION | Stop the drug, assessment the same day |
Back pain in the on-demand trials ran 5 percent at 10 mg and 6 percent at 20 mg against 3 percent on placebo, with myalgia at 4 and 3 percent. The label describes it precisely: diffuse bilateral lower lumbar, gluteal, thigh or thoracolumbar muscular discomfort, worse on lying down, generally starting 12 to 24 hours after the dose and typically gone within 48. Paracetamol or an NSAID covered most cases. Severe back pain was reported at a low frequency, under 5 percent of all such reports, and roughly 0.5 percent of men on the on-demand route stopped the drug because of it. Skeletal muscle PDE11 is the usual suspect, and suspect is the accurate word - tadalafil is only 14-fold more selective for PDE5 over PDE11A1, which makes the theory plausible and unproven.
Everything else common is vascular and shared across the class: headache in 11 percent at 10 mg and 15 percent at 20 mg against 5 percent on placebo, then dyspepsia, flushing and nasal congestion behind it. Daily 5 mg is generally quieter than a full on-demand tablet, and there is nothing to be won by tolerating a dose that produces a headache every single time.
The stops carry no hedging. An erection past four hours needs an emergency department that hour, because trapped blood damages tissue permanently, and sickle cell disease, myeloma and leukaemia raise the risk. Vision lost suddenly in an eye means stopping the tablet and same-day assessment, since NAION presents that way. Hearing that drops away, with or without ringing, gets the same response. Chest pain after a dose is never met with a nitrate from a drawer at home.
Two prescriptions live in one molecule: 5 mg every day, or 10 mg before the occasion
Both routes carry their own trials and their own label wording. The choice turns on how often sex happens and how much the timing itself gets in the way.
| Route | Label dose | What decides it |
|---|---|---|
| On demand | 10 mg before activity; range 5-20 mg | Sex once or twice a week, loosely planned |
| Once daily, ED | 2.5 mg to start, 5 mg on response | Frequent sex, or dislike of timing a tablet |
| Once daily, BPH | 5 mg at about the same time each day | Urinary symptoms, with or without ED |
| Frequency limit | One dose in 24 hours on either route | Never a second tablet because the first hour felt quiet |
On demand, the label opens at 10 mg taken before anticipated sexual activity, adjusted to 20 mg or down to 5 mg on how the first attempts go, once per day at most. Maximum plasma concentration lands at a median of two hours and onset for most men is half an hour to an hour, so a tablet swallowed as the evening starts is already behind the evening.
The once-daily route for erectile dysfunction opens lower: 2.5 mg at about the same time each day, raised to 5 mg on efficacy and tolerability. Four or five days of dosing brings levels to steady state, so a fair verdict on this route takes a week. Some couples pick it for a reason no pharmacokinetic argument covers - swallowing a tablet in front of a partner is an announcement, and a daily dose removes the announcement.
Monthly arithmetic separates the two routes far more than efficacy does. Thirty tablets a month against four to twelve is a different bill, and which one wins depends entirely on frequency. The Canadian Urological Association reviewed the head-to-head evidence and declined to recommend daily dosing in preference to on-demand for ordinary erectile dysfunction, while listing the patient-side reasons that pull individual men towards it: spontaneity, less anticipatory anxiety, partner preference, coexisting urinary symptoms.
Twenty milligrams belongs to a man who gave 10 mg an honest run at sensible timing and came up short. It repairs nothing about a badly timed evening.
Seventeen and a half hours of half-life, and where the 36-hour claim was measured
The long tail is the only real argument for preferring this molecule over the two short-acting ones.
Absorption
Readily absorbed. Maximum concentration at a median of 2 hours. Neither rate nor extent of absorption is influenced by food.
Distribution
Apparent volume of distribution about 63 L; 94 percent protein-bound at therapeutic concentrations.
Metabolism
Hepatic, predominantly CYP3A4, to a methylcatechol metabolite with negligible activity.
Excretion
Roughly 61 percent faecal and 36 percent urinary, as metabolites. Mean terminal half-life 17.5 hours.
Mean terminal half-life is 17.5 hours and mean oral clearance 2.5 L/hr. Elimination is hepatic, predominantly CYP3A4, to a methylcatechol metabolite with no meaningful activity of its own; roughly 61 percent of the dose leaves in faeces and about 36 percent in urine. Ninety-four percent of drug in plasma is protein-bound. Neither the rate nor the extent of absorption changes with food, and that one property is why the molecule suits men whose evenings start late.
Advertising's 36-hour figure was measured in a trial. Men on 20 mg were asked about attempts inside defined windows after the dose: at 33 to 39 hours, 64 percent reported at least one successful attempt against 37 percent on placebo, and at 22 to 26 hours it ran 61 against 37. Both halves of those pairs repay attention. Placebo was not zero, and treatment was not everybody.
It buys availability, not an erection. Arousal still has to happen.
Which is exactly why the men who remember the 36 and skip the 30 to 60 minute onset are the ones who conclude the drug failed.
The 5 mg daily tablet is also the prostate dose, and one label sentence gets misread constantly
One tablet, two licences, and a piece of label wording that reliably frightens men off a treatment they are eligible for.
Five milligrams once daily is approved for the signs and symptoms of benign prostatic hyperplasia, and the same 5 mg covers a man who has both BPH and erectile dysfunction. Where BPH treatment is started together with finasteride, the label caps the combination at 26 weeks, because the incremental benefit of tadalafil decreases from week 4 to week 26 and beyond 26 weeks is unknown. In the study behind that wording, total IPSS fell 5.2 points against 3.8 on finasteride with placebo at 12 weeks, with separation already visible at week 4.
Now the sentence that gets mangled. Tadalafil is not recommended in combination with an alpha-blocker for the treatment of BPH, because the efficacy of that combination has not been adequately studied and because two vasodilators together lower blood pressure. Tadalafil alone for BPH is approved and unremarkable. Read the compressed version and it sounds as though a man on tamsulosin can never have tadalafil at all, which is wrong: he can be treated for erectile dysfunction, stable on the alpha-blocker first and started at the lowest dose, with a conversation about dizziness on standing.
PDE5 is not confined to penile tissue. It also sits in prostatic and bladder-neck smooth muscle, which is how a daily erectile dysfunction tablet acquired a urological licence. Adcirca and Alyq are the same molecule licensed for pulmonary arterial hypertension on a different schedule under specialist care, and raiding either supply in either direction is wrong: a lung prescription is no spare erectile dysfunction stock, and a leftover 10 mg does nothing for lung pressure.
Food is genuinely irrelevant on this drug; five units of alcohol are not
Freedom from the food rule is real here, and it is the thing most men have actually heard about the drug. The alcohol sentence is less well known.
Tadalafil may be taken with or without food, and the label says that without qualification. No fasting, no arithmetic about how fatty the meal was. Sildenafil is the molecule where a heavy meal shifts the peak, and the numbers behind that live in the timing and food briefing; importing its rules here adds a superstition and nothing else.
Alcohol is the part of this section that earns attention. Tadalafil and alcohol are both mild vasodilators, and the label names substantial amounts - five units or more - alongside alpha-blockers and antihypertensives as the setting where symptomatic hypotension turns up. A glass with dinner is not that setting. A long night is. Heavy drinking also blunts arousal, which is the one input no PDE5 inhibitor supplies.
Grapefruit juice inhibits CYP3A4 weakly next to a prescription inhibitor, but a litre-a-day habit is worth naming at the appointment. It has never improved anyone's dose.
Renal function and CYP3A4 inhibitors stretch the interval instead of shrinking the dose
Where most labels shrink a milligram figure, this one often widens the gap between doses. It catches people out.
Ceilings worth checking before the prescription is written
- Potent CYP3A4 inhibitors, including ritonavir, ketoconazole and itraconazole: on demand, 10 mg maximum every 72 hours; once daily, 2.5 mg maximum.
- CYP3A4 inducers such as rifampin and some anticonvulsants: exposure falls and a previously adequate dose can quietly fail.
- Creatinine clearance 31-50 mL/min: start 5 mg once daily, maximum 10 mg every 48 hours.
- Clearance under 30 mL/min or haemodialysis: maximum 5 mg every 72 hours, and once-daily use is not recommended.
- Child-Pugh A or B: up to 10 mg on demand. Child-Pugh C: not recommended.
Creatinine clearance runs the on-demand ceiling, and it does the work by lengthening the gap. At 31 to 50 mL/min the start is 5 mg no more than once a day, with a maximum of 10 mg not more often than every 48 hours. Below 30 mL/min, including men on haemodialysis, the maximum is 5 mg once every 72 hours, and once-daily dosing is not recommended at all. A specific finding sits inside that work: at 10 mg, back pain was the limiting adverse event in men with moderate renal impairment, and at 5 mg its incidence and severity were no different from the general population.
The hepatic wording is shorter. Mild to moderate impairment allows up to 10 mg on demand. Child-Pugh C is not recommended, and once-daily use has not been studied in severe impairment.
Potent CYP3A4 inhibitors do the same job from the drug side. With ritonavir, ketoconazole or itraconazole on the list, on-demand tadalafil is limited to 10 mg no more often than every 72 hours, and the once-daily dose must not exceed 2.5 mg. Inducers push the other way; rifampin and several anticonvulsants can cut exposure enough that a dose which used to work quietly stops working. That is the question to ask before anyone steps up to 20 mg.
Forty-eight hours, and the reason the figure is not twenty-four
Nothing here bends, which is why it sits near the front of the page instead of in a warnings block at the end.
Organic nitrates in any form are a contraindication: nitroglycerin tablets, sprays, ointments and patches, isosorbide mononitrate and dinitrate on a schedule, and the amyl or butyl nitrite bottles sold as poppers. Both act on the nitric oxide pathway that tadalafil defends downstream, and the pair can produce life-threatening hypotension.
The interval is where that number comes from and where readers lose it. The interaction study gave 150 men aged 40 and over tadalafil 20 mg daily for seven days, then a single 0.4 mg sublingual nitroglycerin dose at set points afterwards: 2, 4, 8, 24, 48, 72 and 96 hours. A significant blood pressure interaction showed up at every point up to and including 24 hours. At 48 hours most haemodynamic measures no longer showed it. Hence the label sentence - where a nitrate is medically necessary in a life-threatening situation, at least 48 hours should elapse, and the nitrate is then given under close medical supervision with haemodynamic monitoring.
Sildenafil's equivalent figure is 24 hours. The difference is half-life arithmetic and nothing more; neither interaction is the milder one.
Which leaves an emergency team needing exactly two facts: the name of the tablet and the hour it went down. Riociguat is contraindicated on the same pathway. Alpha-blockers and other antihypertensives belong to a different category of problem - permitted, with the man stable on the other drug first and tadalafil started at the lowest dose.
Compounded troches, gummies and the subscription supply
A large share of the tadalafil taken now arrives by subscription, and part of that is compounded: troches, dissolvable tablets, flavoured gummies made up by compounding pharmacies. Compounded products are not FDA-approved, and nobody has run bioequivalence on that troche against the tablet the trials used. Ten milligrams printed on a compounded label and the 10 mg in the dosing section above are two different claims, and the renal, hepatic and CYP3A4 ceilings were all written for the tablet.
At the other end of the same market sit supplements sold for erections, where regulators keep finding undeclared tadalafil or sildenafil. For a man on a nitrate who believes he has bought a herbal capsule, that is the interaction at the top of this page arriving with no warning attached.
If the obstacle is money rather than pharmacology, the levers are tablet count, route and pharmacy. Going back to sildenafil, which costs a fraction per tablet, is a legitimate clinic conversation and not a demotion. Vardenafil is the third option, with a cardiac rhythm question attached to it.
Last Updated
Straight talk
Your questions, answered plainly
Answered by Dr. Marc Vidal, MD · Internal medicine & clinical pharmacology
Letters about tadalafil usually arrive in the wrong order: the 36-hour figure in the first line, the nitrate spray somewhere near the signature. These replies are teaching, and none of them is a prescription for whoever wrote in.
No. The figure describes how long the drug can help you respond to arousal. In the trial behind it, 64 percent of men on 20 mg reported a successful attempt at the 33 to 39 hour point against 37 percent on placebo, and nothing at all happens without stimulation. Where an erection does pass four hours, that is priapism and it needs an emergency department the same hour, because trapped blood damages tissue. Rare, and the one number worth keeping cold. The long tail has a second consequence people miss: a nitrate is still a problem the next calendar day, so if you ever need urgent care, carry the name of the tablet and say what time you took it.
He can have 5 mg each morning or 10 mg when we need it. How do we decide?
Start from how the month actually looks. If sex is once or twice a week and loosely planned, 10 mg on demand is simpler and usually cheaper, because that is four to twelve tablets a month against thirty. If the business of taking a tablet in front of you is itself the obstacle, the daily route removes it, and after four or five days the level is steady. Give either one a proper week before judging it. One extra point: if he also has urinary symptoms, 5 mg daily is licensed for those in its own right, so a single tablet can be doing two jobs. Whichever you try, do not run both routes, and take the decision back to his prescriber if anything else on his list lowers blood pressure.
I keep a nitroglycerin spray for occasional angina. Can I still take 10 mg at the weekend?
No, and no modified version of it either. The spray is a nitrate, and the two together can send blood pressure down far enough to be dangerous. The label permits a nitrate after tadalafil only where it is medically necessary in a life-threatening situation, and then only once at least 48 hours have passed, under monitoring. A weekend tablet does not create a safe pocket inside that window, because the drug is still measurable across it. If you need the spray, this class is the wrong one for you until the clinician managing your angina says otherwise. I would rather you kept the spray than traded it for an erection tablet.
He already takes tamsulosin for his prostate. Is the daily 5 mg allowed?
It is a discussion for his prescriber and not something to add at home. Two separate label sentences get tangled here. Tadalafil 5 mg daily is approved for the urinary symptoms of an enlarged prostate on its own. What the label does not recommend is running tadalafil together with an alpha-blocker to treat those symptoms, because that combination has not been adequately studied and both drugs lower blood pressure. Neither sentence is the nitrate ban, which is absolute. If he is stable on tamsulosin, a prescriber may still start tadalafil low for erectile dysfunction and watch for dizziness on standing. Bring both boxes to the visit.
I get a dull backache the day after a tablet. Have I damaged something?
Almost certainly not. Back and muscle ache is the characteristic nuisance on this drug, reported by 5 to 6 percent of men in the trials. It generally appears 12 to 24 hours after the dose, feels muscular and diffuse across the lower back, buttocks or thighs, is worse lying down, and clears within about 48 hours. Paracetamol or ibuprofen is enough for most men. It is not a kidney warning. If it turns up after every dose and spoils the following day, that is a reasonable argument for trying sildenafil or vardenafil instead, since neither does this to the same degree. Tell the prescriber if the pain is severe or fails to settle.
We eat late. Does a heavy dinner spoil it the way it spoils Viagra?
No. Neither the rate nor the extent of absorption changes with food, which is one of the honest advantages of this molecule and a good reason to pick it if your evenings start at eleven. Take it with dinner if that suits you. Do keep the front end in mind: onset is 30 to 60 minutes and the peak sits at a median of two hours, so it is not instant. The empty-stomach rule belongs to sildenafil. Alcohol is the part worth watching here. A glass is usually unremarkable, while five units or more together with anything else that lowers blood pressure is where men end up lightheaded on standing.
My creatinine is high. Can I take 5 mg every morning?
Probably not, if the impairment is more than moderate, and it is the creatinine clearance rather than the creatinine alone that decides. Between 31 and 50 mL/min the on-demand dose starts at 5 mg and the maximum is 10 mg no more often than every 48 hours. Below 30, or on dialysis, the maximum is 5 mg every 72 hours and the daily route is not recommended at all. Feeling well does not override the number. There was a specific finding in that group: at 10 mg, back pain was the limiting problem in men with moderate impairment, and at 5 mg it was not. Take your most recent lab sheet to the appointment. The liver matters too, since CYP3A4 does the clearing.
He is on ritonavir. Does that change the 10 mg?
Yes, and it changes the interval as much as the number. Ritonavir is a potent CYP3A4 inhibitor and it pushes tadalafil exposure up. With a drug like that on the list, on-demand tadalafil is limited to 10 mg no more often than every 72 hours, and the once-daily route is capped at 2.5 mg. Ketoconazole and itraconazole sit in the same bucket. This is not something to improvise by breaking tablets at the kitchen table, and the label separately says do not split them. Let the clinician who manages the antiviral write the interval, and have the erectile dysfunction dose reviewed in the same week if that antiviral list changes.
We usually open a bottle of wine. Is that a problem?
A glass or two with dinner is unremarkable for most men. Both alcohol and tadalafil widen blood vessels a little, so a heavy session can leave him lightheaded on standing, and it will also blunt the arousal the tablet depends on, which works directly against the reason he took it. The label singles out substantial amounts, five units or more, in the same breath as alpha-blockers and blood pressure medicines. If the room tilts when he stands up, the answer is less wine and not a second tablet. None of this touches the nitrate situation, which stays absolute whether or not there is wine on the table.
He had a heart attack last year. Is this off the table permanently?
Not automatically. The first question is whether his heart is up to sex, which is roughly the exertion of two flights of stairs, and many men are cleared after an uncomplicated recovery. The order matters: cardiology view first, full medicine list second, dose last. The hard stop is a nitrate. If he still uses nitroglycerin or takes a scheduled nitrate, tadalafil is contraindicated, and the 48-hour rule makes clever timing pointless. I will not pick 5 mg daily or 10 mg on demand for a man I have not examined. Take him to whoever knows the infarct. Plain-language background is at https://medlineplus.gov/druginfo/meds/a604008.html.
The table lists four pharmacies. Which is cheapest in Barcelona?
None of them. Walmart, Sam's Club, Meijer and Cost Plus Drugs are American counters, listed so a reader can compare ten generic 10 mg tablets inside that one market. Spanish addresses are outside their reach, and this page dispenses nothing whatsoever. Here the route is an appointment, a prescription and whichever farmacia is nearest. I am not going to put a euro figure on your neighbourhood either, because those numbers move month to month. If money is the real question, the comparison worth making is between the two routes rather than between two shops: thirty tablets a month against a handful, weighed against how often you actually need one.
Why does this page talk about 5 mg and 10 mg when the box also comes as 20?
Because those two are the strengths most first prescriptions are written on, and the page is organised around what a first prescription looks like. The full range is on the label: 2.5 and 5 mg for daily use, and 5, 10 and 20 mg on demand. Twenty is a step up after 10 mg has had a fair trial with sensible timing, and 2.5 mg daily is a quieter start that suits some men. Nothing is invented and nothing is being withheld; your prescriber can write any of them. The one thing that is not on the menu is buying 20 mg and halving it, because the label says do not split the tablets and they are not scored.
When would you move a man to Viagra or Levitra instead?
When the ache after every dose costs him more than the problem it solves. When a daily tablet is more medicine than he wants for a fortnightly event. When the monthly cost of the daily route stops making sense against how often he has sex, since sildenafil is markedly cheaper per tablet. Or when a short window is genuinely preferable, because a 36-hour tail is no advantage to everybody. Response rates across the three sit in one band, so this is matching rather than ranking. The PDE5 comparison lines up duration, food and the rhythm footnote that only vardenafil carries. Bring the list, and I will not tell you which is strongest.
Read each reply as a general teaching point, not a plan built for the person who asked. Your own situation - notes, bloods, every medicine you take - belongs in front of a prescriber who can weigh all of it together.