What is the half-life of Viagra? Sildenafil's half-life is 3 to 5 hours: every 3 to 5 hours, the amount in your blood halves. After a tablet taken on an empty stomach, sildenafil reaches its highest level within 30 to 120 minutes (60 minutes in the middle case), then falls away at that rate (EMA product information). Its effect lasts up to about 4 hours, and by the next day only a few per cent of a dose is left on that arithmetic. Age, kidney or liver problems and some medicines keep it in the blood longer.
What does half-life mean for Viagra?
It is the time it takes for the level of a medicine in the blood to drop by half. For sildenafil the label gives a "terminal phase half-life of 3-5 h", and the body clears it mainly through liver enzymes, chiefly CYP3A4. Its main breakdown product is about half as active, reaches about 40% of sildenafil's level and has a half-life of about 4 hours (EMA product information). How long the effect lasts is a separate question, answered below.
How long does Viagra stay in your system?
Most of it is gone within a day. If the level halves every 3 to 5 hours from its peak, this is roughly what is left:
| Half-lives after the peak | Hours (at 3 to 5 h each) | Share of the peak level left |
|---|---|---|
| 1 | 3 to 5 | 50% |
| 2 | 6 to 10 | 25% |
| 3 | 9 to 15 | 12.5% |
| 4 | 12 to 20 | about 6% |
| 5 | 15 to 25 | about 3% |
Arithmetic on the half-life in the EMA product information, not a measured curve.
No label says when sildenafil is completely gone, so we do not give a time for that. Whether a test could still find it is a different question: does Viagra show up on a drug test?
Does the half-life tell you how long Viagra works?
No. The effect is a window, not a countdown of the blood level: "The effects of the medicine can last for up to 4 hours. This means that the ability to have an erection can occur during this 4 hour period, but the actual erection will only last for a normal period of time" (healthdirect). In a laboratory study, sildenafil could still produce an erection with sexual stimulation 4 to 5 hours after the dose (EMA product information). It works only with sexual arousal (Viagra CMI), and an erection that lasts more than 4 hours needs the nearest hospital emergency department (healthdirect). More in how long does sildenafil last?
Does 100 mg stay in the body longer than 50 mg?
A little longer, because it starts higher. Between 25 and 100 mg the blood level rises in proportion to the dose, with one half-life for every strength (EMA product information), so 100 mg starts at about twice the level of 50 mg and needs one more half-life, 3 to 5 hours, to fall to the same point. More in 50 mg vs 100 mg Viagra.
What makes sildenafil stay in the body longer?
Older age, severe kidney problems, liver problems and some medicines. The label measures these as more sildenafil in the blood over time (exposure), and for most suggests a lower starting dose:
| Who | What the label found | What the label suggests |
|---|---|---|
| Men aged 65 or over | About 90% higher blood levels (clearance reduced) | No dose change needed |
| Severe kidney impairment | Exposure about doubled (up 100%) | Consider 25 mg |
| Liver cirrhosis (mild to moderate) | Exposure up 84% | Consider 25 mg |
| Taking erythromycin, saquinavir or similar medicines | Exposure up 182% and 210% | Consider 25 mg |
| Taking ritonavir | Exposure up 11-fold | Not advised; never more than 25 mg in 48 hours |
Source: EMA product information, sections 4.2, 4.5 and 5.2.
Ritonavir shows what that means in hours: 24 hours after a 100 mg dose, the blood level was still about 200 ng/mL, against about 5 ng/mL for sildenafil alone (EMA product information). The Australian leaflet lists antifungals, some antibiotics and HIV medicines among those to tell your doctor about (Viagra CMI).
Why only one tablet a day?
Because that is the label's limit: "The maximum recommended dosing frequency is once per day" (EMA product information), and "You should not take any more than one sildenafil tablet in 24 hours" (healthdirect). If a dose is not enough, tell your doctor, who may change it (Viagra CMI); do not take a second tablet. More in can I take Viagra twice in one day?
How does it compare with Cialis?
Tadalafil, the medicine in Cialis, stays far longer: "the mean half-life is 17.5 hours in healthy subjects" (EMA Cialis product information), and it "has been proven to be effective for up to 36 hours" (Cialis CMI).
The two are not taken together: "Do not take sildenafil if you are taking other medicines for ED" (healthdirect). More in can you mix Viagra and Cialis?
The short answer
Sildenafil's half-life is 3 to 5 hours: the level in your blood halves at that rate, and only a few per cent is left by the next day. The effect lasts up to about 4 hours. Kidney or liver problems and some medicines keep it in the blood longer; one tablet a day is the limit. More on doses is in our dosage guide.
