Does grapefruit juice enhance the effects of Viagra? It raises the amount of sildenafil in the blood a little, but nothing shows that it improves the erection. In the one study of the pair, grapefruit juice raised total exposure to sildenafil by 23%, left the peak level essentially unchanged and made the medicine less predictable, and the authors advised avoiding the combination. It affects the other erectile dysfunction tablets too.
Does grapefruit juice make Viagra work better?
Nothing shows that it does. What grapefruit changes is how much sildenafil reaches the blood: "Grapefruit juice is a weak inhibitor of CYP3A4 gut wall metabolism and may give rise to modest increases in plasma levels of sildenafil" (EMA — Viagra). CYP3A4 is the main enzyme that breaks sildenafil down, and only about 41% of a tablet's dose reaches the bloodstream (EMA — Viagra), because so much is broken down on its way in; grapefruit juice contains inhibitors of that enzyme in the gut (Jetter et al., 2002). More sildenafil is not a better erection: in the label's studies, 200 mg "did not result in increased efficacy", but headache, flushing, dizziness, indigestion, nasal congestion and altered vision became more common (EMA — Viagra). The grapefruit study measured blood levels, not erections.
How much does grapefruit juice raise sildenafil levels?
By about a quarter, in the one study that measured it. Twenty-four healthy men took a single 50 mg dose of sildenafil twice, once with water and once with grapefruit juice: a 250 mL glass an hour before the tablet and another with it. With the juice, total exposure to sildenafil rose by 23%, while the peak level was "essentially unchanged"; the peak tended to come later (a median of 1.13 hours after the dose instead of 0.75), and men differed widely from one another. The authors concluded: "Sildenafil pharmacokinetics may become less predictable with grapefruit juice. Although patients usually will not be endangered by concomitant use of grapefruit juice, it seems advisable to avoid this combination" (Jetter et al., 2002). For scale, the label reports that the antibiotic erythromycin raised sildenafil exposure by 182% and the HIV medicine ritonavir elevenfold (EMA — Viagra): which antibiotics affect Viagra?
Is it dangerous to take Viagra with grapefruit juice?
Usually not, in the study authors' words, but it is best left out around a dose. A higher level means more chance of the usual side effects: headache, facial flushing, a blocked nose and indigestion (healthdirect — ED medicines). The Australian Viagra leaflet does not mention grapefruit; the warning sits in the product information for prescribers (Viagra CMI; EMA — Viagra). The usual limits still apply: one sildenafil tablet in 24 hours, and an erection lasting more than 4 hours needs the nearest hospital emergency department (healthdirect — Sildenafil).
How long should you leave between grapefruit and Viagra?
No sildenafil label gives a waiting time, so "wait 24 hours" is not a Viagra rule. The 24-hour line belongs to avanafil: "Patients should be advised to avoid grapefruit juice within 24 hours prior to taking avanafil" (EMA — Spedra). The effect does outlast the glass. A review of grapefruit interactions notes that the whole fruit counts as well as the juice, and that with felodipine, a blood-pressure medicine, juice taken 10 hours before still gave half the maximum effect, and 24 hours before a quarter (Bailey et al., 2013). That was not a sildenafil study.
Does grapefruit affect Cialis, vardenafil and avanafil?
Yes, and two of those labels go further than Viagra's. All four are PDE5 inhibitors available in Australia on prescription (healthdirect — ED medicines).
| Medicine | What the label says about grapefruit |
|---|---|
| Sildenafil (Viagra) | "Modest increases" in sildenafil levels (EMA — Viagra) |
| Tadalafil (Cialis) | On the Australian leaflet's interaction list (Cialis CMI); use "with caution", side effects "might be increased" (EMA — Cialis) |
| Vardenafil | "The combination should be avoided" (EMA — Levitra) |
| Avanafil (Spedra) | Avoid it in the 24 hours before a dose (EMA — Spedra) |
Taking two of these medicines together is a separate question, and no label allows it: can you take Viagra and Cialis together?
Do other citrus fruits do the same?
Some can, with the medicines grapefruit affects. The chemicals responsible are furanocoumarins, and the same review says "Seville oranges, (often used in marmalades), limes and pomelos also produce this interaction", while sweet oranges such as navel or valencia "do not contain furanocoumarins and do not produce this interaction" (Bailey et al., 2013). The review's text does not name sildenafil, and this page found no study of those fruits with it; the review also notes that the interaction "is drug-specific and is not a class effect".
The short answer
Nothing shows that grapefruit juice makes Viagra work better. It raises the level of sildenafil modestly and less predictably, so leave it out around a dose; with vardenafil and avanafil the labels say to avoid it. A heavy meal and a lot of alcohol matter too: foods to avoid with Viagra and can you drink alcohol with Viagra? Every other combination is in our guide to taking Viagra or Cialis with other medicines.
