Medication guide

Tadalafil (Cialis): the 36-hour window and the daily low dose

Tadalafil is the active ingredient in Cialis and in FDA-approved generics. It is a PDE5 inhibitor, like sildenafil, so sexual stimulation is still required and nitrates are still forbidden. The difference patients notice is time. Erectile function can remain improved, compared with placebo, for up to 36 hours after an as-needed dose. That is a window of opportunity, not an erection that lasts 36 hours.

Two regimens, not one sliding scale

U.S. labeling describes two separate ways to use tadalafil for erectile dysfunction. They are not combined.

As needed

The usual starting dose is 10 mg before sexual activity. Based on response and side effects, the prescriber may increase it to 20 mg or decrease it to 5 mg. The maximum frequency is once per day. Improvement versus placebo has been shown out to 36 hours, so a Friday dose may still be relevant on Saturday. The onset is often 30 minutes or more, and some people need closer to 2 hours for the full effect. Taking it without regard to meals is allowed, which is a practical advantage over sildenafil when dinner is a high-fat meal.

Once daily

The starting dose for once-daily use in erectile dysfunction is 2.5 mg, taken at about the same time every day, without regard to the timing of sex. It may be increased to 5 mg. The point of the low dose is a steady background level so that sexual activity does not have to be scheduled around a tablet. It is not a stronger erection medicine milligram for milligram. Someone who takes the daily tablet does not also take a 10 mg or 20 mg tablet that day.

For signs and symptoms of benign prostatic hyperplasia, the labeled once-daily dose is 5 mg. The same 5 mg dose is used when erectile dysfunction and prostate symptoms are being treated together. In that prostate indication, labeling says not to combine once-daily tadalafil with alpha-blockers. Kidney disease changes these limits: once-daily use is not recommended when creatinine clearance is under 30 mL/min. Those adjustments are the prescriber’s.

What “endothelial support” does and does not mean

PDE5 is present in blood vessels, and researchers have studied whether daily tadalafil changes markers of endothelial function. That research is not the same thing as an FDA-approved claim that 2.5 mg or 5 mg repairs arteries. The approved reasons to consider the daily dose are erectile dysfunction on a continuous schedule and, at 5 mg, urinary symptoms from an enlarged prostate. A clinician chooses daily versus as-needed from how often you want to be sexually active, whether prostate symptoms are part of the problem, side effects, kidney function, and every other drug you take. Expecting a low dose to replace blood-pressure treatment, a statin, or smoking cessation is not what the label supports. Those habits are covered on the lifestyle page.

Side effects that are more typical here

Headache, indigestion, back pain, muscle aches, flushing, and nasal congestion are the reactions most often listed. Back pain and myalgia tend to show up 12 to 24 hours after a dose and usually settle within 48 hours. That delay surprises people who felt fine the evening they took it. Sudden vision loss, sudden hearing loss, and an erection lasting longer than 4 hours are the same emergencies as with the other drugs in this class. See the side-effect guide.

Other label limits worth knowing

• With potent CYP3A4 inhibitors such as ketoconazole or ritonavir, as-needed tadalafil is limited on the label to 10 mg and not more often than every 72 hours. Once-daily use is limited to 2.5 mg.
• Substantial alcohol adds to dizziness and a drop in blood pressure. The interaction page gives the practical framing.
• The cardiovascular groups for whom tadalafil is not recommended, including a heart attack within 90 days and a stroke within 6 months, are listed on the cardiac page.

Generic price pattern

FDA-approved generic tadalafil is widely available in both the low daily strengths and the as-needed strengths. Cash prices are often much lower than brand Cialis and still vary by pharmacy, strength, and quantity. Compare like with like. A daily 5 mg prescription is not a substitute, tablet for tablet, for a 20 mg as-needed prescription.

Related: the comparison matrix and the sildenafil guide.

Sources

• Tadalafil tablets prescribing information: as-needed and once-daily dosing, 36-hour efficacy window, food, nitrate 48-hour emergency language, back pain timing, and BPH dosing.