ED medication works well for the majority of men who try it. PDE5 inhibitors like Sildenafil and Tadalafil are effective for around 60 to 70% of men with erectile dysfunction.1 But when they don't seem to be working as expected, the medication might not always be the reason why. Research suggests that incorrect use is responsible for the majority of treatment issues.2 Here's six common ED medication mistakes and what you can do to avoid them.
1. Taking Sildenafil on a Full Stomach
This is one of the most common reasons Viagra or Sildenafil doesn't produce the intended effect. A heavy, high-fat meal can delay absorption by around an hour and reduce peak blood levels by roughly 29%, according to pharmacokinetic studies.3 If you've got an indulgent meal planned, it's best to wait before taking the tablet.
The fix: Take Sildenafil on an empty stomach or after a light meal for the fastest, most reliable onset.4 If you've eaten a large meal, allow a couple of hours before taking it. Tadalafil is less affected by food,5 so if you don't want to plan around mealtimes, it may be a better choice for you.
2. Not Waiting Long Enough for It to Work
Sildenafil doesn't work instantly. It typically takes 30 to 60 minutes to reach full effect.4 Rushing things is a common (but understandable) ED medication mistake. If you take a tablet and try to be intimate straight away, the medication hasn't had time to work in your body.
The fix: Plan ahead. Take Sildenafil about an hour before you anticipate sexual activity. Its effects last for four to six hours,4 so there's no need to time things down to the minute. If you'd prefer not to plan at all, Tadalafil Daily is taken every day and stays active continuously, removing the need to time doses around sex.5
3. Drinking Too Much Alcohol
A bottle of beer or glass of wine is unlikely to have an effect. But heavier drinking is likely to cause some issues. Alcohol is a depressant that reduces blood flow and dulls arousal, directly working against what your ED medication is trying to achieve. It can also lower blood pressure alongside the medication, increasing the risk of dizziness or headaches.4
The fix: Try to keep drinking to a minimum when you're planning to take ED medication. If a few drinks are part of your evening plans, consider taking Tadalafil instead. It has a much longer window of activity (up to 36 hours)5 so you can take it earlier in the day, well before you start drinking.
4. Expecting It to Work Without Arousal
This is a big misconception. Sildenafil, Tadalafil and other PDE5 inhibitors don't make you feel more aroused. They work by enhancing blood flow in response to sexual stimulation.4,5 Without arousal, the reaction in your body that these medications support doesn't start.
It's a fairly common belief, even for people who have been prescribed ED medication. One study of 100 consecutive sildenafil non-responders found that 12% of men were unaware that sexual stimulation was needed for the medication to work.6
The fix: Give yourself time to get in the mood and remember that the medication isn't a shortcut. If anxiety is getting in the way of arousal, that's worth discussing with your prescriber, as psychological factors can reduce the effectiveness of ED treatment.2
5. Giving Up After One Try
It's not unusual for ED medication to fall short the first time. Nerves, unfamiliar side effects, and not yet knowing the right timing for your body can all play a part. Clinical guidelines recommend trying at least six to eight doses of a PDE5 inhibitor before being classified as not responding to the medication.7
One study found that educating men who had initially not responded led to a successful outcome in around a third of cases, with other research reporting salvage rates of up to 55%.2,6
The fix: Be patient and give yourself several attempts in low-pressure situations. If you're not sure which treatment suits you best, our ED Trial Pack lets you compare different treatments side-by-side so you can find the right fit without committing to a full course.
6. Sticking With the Wrong Dose or Wrong Treatment
The standard starting dose for Sildenafil is 50mg, but that's not the right dose for everyone.4 Some men need 100mg for a noticeable effect, while others do well on 25mg. Equally, Sildenafil and Tadalafil work in the same way but have different profiles.
If one isn't working for you, that doesn't mean all ED medication won't work either. Research suggests that up to 60% of men who don't respond to one PDE5 inhibitor find that another works after switching to it.8
The fix: Speak to your prescriber about dose adjustment before writing off a treatment. Clinical guidelines advise titrating (gradually increasing) the dose to find the optimal level for each patient.7
For instance, if you've given Sildenafil a fair try and it's still not delivering the effects you're looking for, switching to Tadalafil (or vice versa) is a sensible next step.
You can read more about the differences in our Sildenafil vs Tadalafil comparison.
Quick Tips for Getting the Best From Your ED Treatment
A few small habits can make a genuine difference to how well your medication works:
Time it right. Take Sildenafil roughly an hour before sexual activity on a relatively empty stomach.3,4
Limit alcohol. One or two drinks are fine. More than that and you're likely working against the medication.4
Stay consistent. Try a medication several times before judging its effectiveness.7
Look at the bigger picture. Exercise, sleep, stress management and cardiovascular health all influence erectile function alongside your medication.7
Talk to your prescriber. If it's not working after multiple fair attempts, a dose change or medication switch could be the change you need.8
When to Seek Further Advice
ED medication is highly effective when taken correctly, and most ED medication mistakes can be solved with straightforward changes.
But if you've addressed all of the points above and you're still not seeing results, there may be an underlying cause for ED that needs investigating. Conditions like diabetes, cardiovascular disease, low testosterone, or the side effects of other medications can all reduce how well PDE5 inhibitors work.1,7
Speaking to your prescriber and GP should be the next step.
Frequently Asked Questions
Why isn't my Viagra working?
The most common reasons are taking it on a full stomach, not waiting long enough before sexual activity, drinking too much alcohol, or expecting it to work without sexual arousal.2,6
Try adjusting your timing and diet first, and give it at least six to eight attempts before concluding it isn't effective.
Can I take Sildenafil with food?
You can, but heavy or high-fat meals can delay how quickly it works and reduce its peak effect.3 For best results, take it on an empty stomach or after a light meal.
How long should I wait for ED medication to kick in?
Sildenafil typically takes 30 to 60 minutes.4 Tadalafil can take a similar time but stays active for up to 36 hours, offering a much wider window.5 Both still require sexual stimulation to work.
What should I do if Sildenafil doesn't work the first time?
You should give it at least six to eight attempts before deciding it's not right for you. See if any of the changes in this article can be made such as timing it around meals and reducing alcohol intake. If it still isn't working after multiple attempts, talk to your prescriber about adjusting the dose or possibly switching to another treatment.7,8
Is Tadalafil better than Sildenafil?
Neither is objectively better. They work in the same way but have different durations and food interactions. Sildenafil is shorter-acting (4 to 6 hours) and best taken on an empty stomach. Tadalafil lasts much longer (up to 36 hours) and is less affected by food.4,5 The right choice depends on your personal lifestyle and preferences.
References
- Hatzimouratidis K, Giuliano F, Moncada I, et al. EAU guidelines on erectile dysfunction, premature ejaculation, penile curvature and priapism. European Association of Urology; 2023. See also: Andersson KE. PDE5 inhibitors – pharmacology and clinical applications 20 years after sildenafil discovery. Br J Pharmacol. 2018;175(13):2554–2565. PMID: 29667180.
- Shamloul R, Ghanem H. Erectile dysfunction. Lancet. 2013;381(9861):153–165. See also: Hatzimouratidis K, Hatzichristou D. Treatment strategy for non-responders to PDE5 inhibitors. Korean J Urol. 2006;47(1):9–17. Also: McMahon CG, Smith CJ, Shabsigh R. Treating erectile dysfunction when PDE5 inhibitors fail. BMJ. 2006;332(7541):589–592. PMID: 16528082.
- Nichols DJ, Muirhead GJ, Harness JA. Pharmacokinetics of sildenafil after single oral doses in healthy male subjects: absolute bioavailability, food effects and dose proportionality. Br J Clin Pharmacol. 2002;53(Suppl 1):5S–12S. PMID: 11879254.
- Sildenafil 50mg film-coated tablets. Summary of Product Characteristics (SmPC). Electronic Medicines Compendium (EMC). MHRA. Available at: medicines.org.uk. Accessed April 2026.
- Tadalafil 10mg and 20mg film-coated tablets. Summary of Product Characteristics (SmPC). Electronic Medicines Compendium (EMC). MHRA. Available at: medicines.org.uk. Accessed April 2026.
- Hatzichristou D, Moysidis K, Apostolidis A, et al. Sildenafil failures may be due to inadequate patient instructions and follow-up: a study on 100 non-responders. Eur Urol. 2005;47(4):518–522. PMID: 15774252.
- NICE Clinical Knowledge Summaries. Erectile dysfunction. National Institute for Health and Care Excellence. Available at: cks.nice.org.uk/topics/erectile-dysfunction. Accessed April 2026. See also: Phosphodiesterase-5 inhibitors prescribing information.
- McMahon C. Non-invasive management of primary phosphodiesterase type 5 inhibitor failure in patients with erectile dysfunction. Ther Adv Urol. 2011;3(3):107–118. PMID: 21789098. See also: Carson CC, Hatzichristou DG, Carrier S, et al. Erectile response with vardenafil in sildenafil nonresponders (PROVEN study). BJU Int. 2004;94(9):1301–1309.
This article is intended for informational purposes only and does not replace professional medical advice. Always read the patient information leaflet supplied with your medication and speak to a healthcare professional if you have specific concerns.
Treat ED with Pharmica
Pharmica is one of the top-rated pharmacies in the UK, having helped over 2 million customers and earned a 4.9 out of 5 rating from more than 237,000 customer reviews. We are committed to delivering the highest standards of service, providing convenient online consultations for a range of clinically proven erectile dysfunction treatments with discreet delivery.
In addition, we regularly publish comprehensive health guides featuring information and advice based on the latest medical research via our Health Hub and through our popular email newsletter.