The short answer: when sildenafil or tadalafil seems not to work, the medicine itself is rarely the problem. Far more often it is how it was used, taken too late, on a full stomach, at too low a dose, or without enough arousal. Working through those explanations before concluding the treatment has failed saves a lot of unnecessary disappointment.
You did not give it long enough
Sildenafil needs 30 to 60 minutes to reach effective levels, sometimes longer after food. Taking it and expecting an effect within ten minutes is the single most common mistake. Tadalafil taken as needed also wants at least 30 minutes, and daily tadalafil needs about five days of dosing before it reaches a steady level. Patience is part of the instructions, not an optional extra.
You took it after a heavy meal
A large or fatty meal can substantially slow sildenafil's absorption, delaying and blunting the effect. If your evenings run to a big dinner and wine, that alone can explain a flat result. The practical fix is simple: take sildenafil on a relatively empty stomach, ideally not straight after a heavy meal, and allow the full hour. Tadalafil is not affected by food in the same way, which is one reason a prescriber might suggest switching if meals keep getting in the way, or if the spontaneity of planning around food and timing is itself part of the frustration.
There was not enough arousal
This is the mechanism people most often forget. PDE5 inhibitors do not create an erection; they amplify the body's response to arousal. If the setting is not conducive, if anxiety is high, or if you are expecting the tablet to do the work by itself, the result falls flat, not because the medicine failed, but because there was nothing for it to amplify.
This is not a minor footnote. It is the single biggest reason a tablet appears to fail, and it is precisely why these medicines are prescription-only rather than something you take like a painkiller. The NHS guidance on erection problems makes the same point, that a PDE5 inhibitor only helps you get an erection in response to sexual stimulation. Practically, that means the same things that support arousal in general, feeling relaxed, unhurried, present with a partner and free of distraction, are what let the medicine do its job. A tense, clock-watching attempt to prove the tablet works often becomes the very thing that stops it working.
Anxiety is a particularly common culprit, and it feeds on itself; we cover that loop in performance anxiety and ED.
The dose might be too low
Prescribers usually start at a moderate dose and adjust. If several honest attempts at the right timing, on an empty-ish stomach, with genuine arousal, still fall short, the dose may simply need increasing within the licensed range. That is a conversation with your prescriber, not a cue to take two tablets, doubling up increases side effects without a licensed basis.
Something underlying may need attention
If troubleshooting genuinely does not help, that is useful information rather than a failure. It may point to an underlying cause the tablet cannot address on its own: significant vascular disease, low testosterone, a psychological component, or the effect of another medicine.
This is where a proper assessment earns its place. UK clinical guidance on managing erectile dysfunction sets out a stepped approach: confirm the medicine was used correctly and at an adequate dose, consider a switch between agents, then look for treatable contributing factors such as hormonal, vascular or psychological causes. A minority of men do not respond to tablets at all, and for them there are further options, from vacuum devices to injections or specialist referral. The point is that a tablet not working is the beginning of a fuller assessment, not the end of the possibilities.
Erectile dysfunction can also be an early warning of heart or circulation problems, which is a reason to see your GP rather than just chase a bigger dose, we explain why in ED and heart health.
Alcohol and tiredness quietly get in the way
Two everyday factors deserve a mention because they are so easy to overlook. Alcohol, beyond a drink or two, is a depressant that blunts arousal and dampens the erectile response, so a tablet taken at the end of a heavy night is working against the tide. Tiredness does something similar: fatigue lowers desire and makes arousal harder to sustain. Neither means the medicine has failed, they mean the conditions were not in its favour. Choosing an occasion when you are rested and have not been drinking heavily gives any dose a fairer chance.
When to go back to your prescriber
Go back if a fair trial at the right dose and timing has not worked, if side effects are getting in the way, or if anything about your health has changed. Options include adjusting the dose, switching between sildenafil and tadalafil, changing to a daily pattern, or investigating a cause. It helps to arrive with specifics: how long you waited, whether you had eaten, how many separate occasions you tried, and what the dose was. That turns a vague sense that it did not work into the concrete detail a prescriber needs to make a good decision. Do not stop any other prescribed medicine on your own in the meantime. Treatment that is not working is a starting point for a conversation, not the end of the road.
