Dr. Shamard Charles is a physician-journalist reporting on health policy, public health initiatives, diversity in medicine, and new developments in health care research and medical treatments.

Matthew Wosnitzer, MD, is a board-certified urologic surgeon and physician scientist. He specializes in male infertility.

Penile injection therapy is a proven and FDA-approved medication to help people struggling with erectile dysfunction achieve and maintain an erection. Injection therapy is especially sought after by people who want more immediate erections.

Injectable alprostadil, sold under the brand names Caverject, Edex, and Prostin VR, causes an erection by relaxing the smooth muscle and opening blood vessels in the penis. Alprostadil is also available as a suppository—a solid piece of medicine that dissolves into the urethra—but it is less commonly used due to cost, efficiency, and side effects.

Other prescription medications commonly used in penile injection therapy are Trimix, Bimix, and papaverine, but most people start with Trimix, which contains three main ingredients: alprostadil, phentolamine, and papaverine.

This article will review how these injectable medications are used and what to know about dosage and side effects before you begin treatment.

Penile injectable therapy is a quick, highly effective, and mostly pain-free way to relieve your ED. It is also useful for those who cannot take traditional ED pills or have not had success taking them. 

Before using the drug therapy on your own at home, your healthcare provider will show you how to inject the medication, usually on a urological model of the pelvis or on a video. The process of injections usually follows these steps:

If you prefer, you can use an auto-injector, which is a spring-loaded device that inserts the needle into the penis very quickly, minimizing discomfort. 

The thought of injecting a needle into your penis may sound intimidating, but many people with ED find that the treatment works. Research shows that 70% of people who use penile injection therapy are happy with their results.

Do not take any ED drugs for at least 24 hours prior to your appointment, especially Cialis or Viagra. Traditional ED drugs like these should never be taken with penile injections.

Also, prepare any questions you may have for your urologist or healthcare provider beforehand. It’s worth noting that if you plan on having your partner assist with or perform the injections, they should be present at your teaching appointment.

The slogan often used with penile injection therapy dosing is to go low and slow. This means that your healthcare provider will probably start with a low dosage and increase your dose each time until you get the effect you want.

Adult injections usually start at 1.25 micrograms, but can go as high as 60 micrograms. Your exact dose will be determined by your doctor.

Adults should only take one single dose per day 10 to 30 minutes before intercourse. The maximum recommended number of injections per week is three.

Occasionally, penile injections may cause a dull ache at the injection site, as well as fainting, dizziness, and low blood pressure, but these side effects usually resolve quickly and on their own. Pain can also occur as a side effect of alprostadil, in which case the medication Bimix (papaverine, phentolamine) may be prescribed instead.

If any of these side effects persists, contact a healthcare provider. If your erection persists for more than four hours (a condition called priapism ), seek immediate medical attention. It is advised that you call your urologist and seek care at a local emergency department.

Priapism is more common in formulations that contain papaverine and phentolamine, but once the dosing is established, it rarely occurs.

You should never take an injection if you have taken Viagra, Cialis, or any other oral erectile medication the night before or the morning of your penile injection therapy. The same is true of your teaching appointment with your urologist if they will be administering your first injection.

The medication should be stored in a refrigerator and used within 90 days. Also, always make sure that you keep your medication and syringes out of the reach of children and safely dispose of outdated medicine.

Lastly, a cardiologist should be consulted before using penile injections to ensure safety, especially if a patient has a pre-existing heart problem.

Penile injection therapy is a safe and effective tool to solve your ED problems, but it isn’t for everyone. Injections are less effective in people with vascular disease, uncontrolled diabetes, or high blood pressure.

If injections don’t work after three months of use, contact a healthcare provider. Additional treatment options are available that they can help you explore.

You can expect an erection to develop five to 20 minutes after injection. Erections usually last 30 minutes to an hour or up to orgasm.

Injections are about 80% effective, although some studies have found this number to be as high as 89%.

When injections are performed correctly, they cause minimal pain. Using an auto-injector may also reduce the amount of pain and psychological hesitancy that you experience. Ask your healthcare provider if an auto-injector option is available to you. If there is a reaction to alprostadil with penile pain, then an alternative medication regimen can be selected.

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Coombs PG, Heck M, Guhring P, Narus J, Mulhall JP. A review of outcomes of an intracavernosal injection therapy programme. BJU Int. 2012;110(11):1787-1791. doi:10.1111/j.1464-410X.2012.11080.x

UCSF Health. Patient guide to penile injections.

Bearelly P, Phillips EA, Pan S, et al. Long-term intracavernosal injection therapy: treatment efficacy and patient satisfaction. Int J Impot Res. 2020;32(3):345-351. doi:10.1038/s41443-019-0186-z

Memorial Sloan Kettering Cancer Center. Penile injection therapy.

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