Injection Therapy at Home: The Four-Hour Rule for Priapism

In the last few weeks, three different men asked me some version of the same question. Each of them had been taught to use injection therapy at home. Each of them was doing well with it. And each of them, almost in passing, asked: "How long is too long?"

It is a good question, and it deserves a clear answer. Here it is: if your erection is still firm four hours after you injected, it is an emergency. Go to A&E.

Injection therapy — an injection into the side of the penis that produces an erection — works well for many men when tablets have not. You were taught how to use it after a consultation, and you were probably told about prolonged erections at the time. But that conversation happened in a clinic, in daylight, with a lot of other information. The moment you actually need it may be at two in the morning, alone, and embarrassed.

So this page is for that moment. I want you to know what an erection that will not go down means, why the clock matters so much, what to say when you get to hospital, and how to lower the chance of it happening at all.

Most men who use injections never have this problem. I am not writing this to frighten you away from a treatment that works. I am writing it because this is one of the few situations in my specialty where a few hours genuinely change the outcome — and the men who do well are the ones who acted early.

The one number to remember — four hours

A normal erection from an injection lasts long enough for sex and then fades. An erection that lasts well beyond that, without going down, is called priapism.

The type of priapism that injection therapy can cause is called ischaemic priapism. Blood flows into the penis but cannot flow out. The trapped blood slowly runs out of oxygen, and the erectile tissue starts to suffer. It often becomes painful — but pain is not a reliable guide to how serious it is.

European urology guidelines treat an erection lasting more than four hours as an emergency. Treatment should start as early as possible — ideally within four to six hours. That is why the rule is so simple:

If your own clinic has given you a written plan for prolonged erections, follow it. But never let anything — a plan, a phone call, a message waiting for a reply — delay you going to A&E once you reach four hours.

This page is part of my wider guide to treatment options, and sits alongside my main page on erectile dysfunction.

Why a few hours make such a difference

The damage in priapism depends mostly on one thing: how long it lasts. The guidelines are clear that duration is the strongest predictor of whether erections recover afterwards.

When priapism is treated within 24 hours, most men — between 78 and 100 in every 100 in the studies — get their natural erections back. After about 20 hours, the risk of lasting erection problems rises sharply. By 36 to 48 hours, more than 90 in every 100 men are left with erectile dysfunction, because the tissue has been permanently damaged.

Put simply: the tissue can cope with a short episode, but not with a long one. Every hour you wait at home is an hour the tissue spends without fresh blood.

How likely is this to happen to you?

For most men, the risk is low — but it is not zero, and it depends on which drug you use.

• • Alprostadil
• • is often used on its own. Its official product information reports an erection lasting four to six hours in about 4 in every 100 men, and priapism of six hours or more in about 4 in every 1,000.
• • Mixtures containing papaverine
• • are sometimes prescribed off-licence, meaning they are used outside the terms of their official licence. The guidelines estimate priapism in about 5 in every 100 men using these mixtures, compared with fewer than 1 in 100 using alprostadil alone.
• • Aviptadil with phentolamine
• • is another option. I have not been able to confirm a reliable figure for how often it causes priapism, so I will not quote one. If you use it, ask your prescribing clinic what they know.

These are figures across large groups of men. Your own risk also depends on your dose, on whether you have taken anything else that day, and on your general health.

Lowering your risk — the rules that actually matter

Several things raise the risk of a prolonged erection, and most of them are in your control. These are the points I go through with every man I start on injections.

1. 1. Use exactly the dose you were taught.
2. 1. Your dose was found by starting low and increasing it step by step under supervision. The aim is the lowest dose that works for you. Never raise it yourself because the last erection felt less firm — speak to your clinic instead. Your starting dose is usually worked out in clinic with a supervised test injection, which is often done as part of a penile Doppler ultrasound.
3. 1. Respect the limits on how often you inject.
4. 1. For alprostadil, the product information says no more than once in 24 hours and no more than three times a week. If you use a different drug, check the limits your clinic gave you.
5. 1. Do not combine erection treatments.
6. 1. Do not take a tablet such as sildenafil on the same day as your injection, and never use two injection drugs together unless they were prescribed as one mixture. The alprostadil product information warns specifically that combining treatments can cause prolonged erections.
7. 1. Be honest with yourself about alcohol and drugs.
8. 1. The guidelines list alcohol, cannabis and cocaine among the causes of priapism. There is no reliable figure for how much each one adds to the risk when you also inject, but they are best avoided on the days you use your treatment.
9. 1. Tell your prescriber about every medicine you take.
10. 1. Some medicines can cause priapism on their own, including some antipsychotic medicines and trazodone, an antidepressant. Your prescriber needs the full list to judge your dose safely.

A word about chemsex, too — using drugs such as crystal meth (methamphetamine), mephedrone or GHB during sex. Small published studies of men who developed priapism after using injections recreationally found that most had taken recreational drugs at the time, often methamphetamine, and that chemsex was a common reason for injecting. If you use injections, never combine them with recreational drugs, never go above your prescribed dose, and never inject someone else's medicine. If it does happen, the four-hour rule still applies: go to A&E and tell them what you took. You are there to be treated, not judged.

If it happens — what to do, step by step

If you have injected and your erection is lasting longer than you expected, this is what I want you to do.

1. 1. Know your start time.
2. 1. Make a note of when you injected. It helps to get into the habit of noting the time every time you use your treatment.
3. 1. Watch the clock, not the erection.
4. 1. If it is still firm four hours after the injection, it is time to go — even if it is not very painful and even if it seems to be softening slightly.
5. 1. Go to A&E.
6. 1. Do not wait for the morning, a GP appointment or a reply from your clinic. If your clinic has given you a written plan, follow it, but it must not delay you going to A&E at four hours.
7. 1. Tell them what you use.
8. 1. Say that you use injection therapy for erections, the name of the drug, your dose and the time you injected. Take the box, the prescription or a photo of the label with you if you can.
9. 1. Mention anything else you have taken.
10. 1. That includes any tablets for erections, other medicines, alcohol or recreational drugs. It changes nothing about how seriously they take you, and it helps them treat you safely.

What happens when you get to hospital

Knowing what to expect can make it easier to go. The details vary between hospitals, but the guidelines describe a clear order of treatment.

When priapism follows an injection, the first step is usually an injection of a medicine that narrows blood vessels — such as phenylephrine — into the penis. This helps the trapped blood drain. If that is not enough, the doctor removes blood from the penis with a needle and washes the tissue out. Used together, these two steps resolve the erection in 80 to 100 in every 100 men in the studies, compared with 58 in 100 with the injection alone.

If priapism has lasted a long time, or does not respond, more treatment may be needed — including surgery. This is exactly why getting there early matters: early priapism is usually treated with needles, not an operation.

After an episode — before you inject again

Once the erection has gone down and you are home, it is normal to feel shaken. Some men are tempted to quietly stop their treatment. Others carry on as before. Neither is ideal.

Tell your prescribing clinic what happened before you use your next dose. Your dose may need to be lowered, or something else that day — a tablet, alcohol, another medicine — may explain it. That review is how most men go on to use injection therapy safely again.

If you notice any change in your erections in the weeks afterwards, mention that too. It is useful information, not a failure on your part.

What I want you to take away

Injection therapy is a good treatment, and for most men it is a safe one. The risk of priapism is real but small, and most of it can be lowered by using the right dose, respecting the limits on how often you inject, and not mixing treatments.

If it does happen, there is only one thing to remember: four hours, then A&E. Tell them you use injection therapy, the drug, the dose and the time. Men who act at four hours usually do well. The ones I worry about are the ones who wait.

Your first point of contact for anything else — dose questions, side effects, a review after an episode — is the clinic that prescribed your injections. If you would like a second look at how your treatment is going, I am happy to review it with you.

Common questions about injection therapy and priapism

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