Alprostadil
The injection that treated erectile dysfunction before the pills, and still works when they do not
Alprostadil is prostaglandin E1, a lipid rather than a peptide. Injected into the penis it relaxes smooth muscle and produces an erection without arousal, which is why it still has a place after the oral drugs fail. The same molecule keeps a newborn's ductus arteriosus open.
What is it?
Alprostadil is on this site because it is sold and discussed alongside the peptides used for sexual function, not because it is one: it is prostaglandin E1, a fatty acid. It relaxes smooth muscle in the penis directly, so an erection follows the injection whether or not there is arousal.
The Caverject label starts dosing at 2.5 mcg, or 1.25 mcg when the cause is purely neurogenic such as spinal cord injury, with the first injections given in the clinic and the dose titrated to the lowest that works, no more than three times a week. Its warnings are about what the drug does too well: prolonged erection and priapism, with instructions to seek help after four hours, and penile fibrosis, which calls for stopping the drug.
It is cleared very fast. The label reports that about 80% of circulating alprostadil is metabolised in a single pass through the lungs, which is why it works locally and leaves little behind in the bloodstream.
The trials are old, large and clear. In the label's first study of 153 men, 76% responded on clinical evaluation, and 73% of home injections led to satisfactory intercourse. Injection beats the urethral pellet by a wide margin, which is the most useful thing to know before choosing between them. For men whom tablets fail, a cream added to a PDE5 inhibitor has been tried with some success. For erections with a psychological cause, a 50-man pilot found low-dose injections no better than sex therapy (47% against 58% regained unaided erections).
Its other life is in newborns. Babies born with certain heart defects depend on the ductus arteriosus, a fetal blood vessel that normally closes after birth, and an alprostadil infusion keeps it open until surgery. The Prostin VR label carries a boxed warning: apnoea affects about 10 to 12%, mostly in the first hour and in babies under 2 kg. Studies since suggest lower doses than the label's 0.05 to 0.1 µg/kg/min starting range keep the duct open with less apnoea, and gut side effects track the total dose. Tried in leg ulcers from arterial disease, it did no better than placebo.
Outside those two labels it is given by infusion, mostly in older or regional trials. In advanced peripheral arterial disease, pooled placebo-controlled trials found more ulcer healing or pain relief (47.8% against 25.2%) and fewer major amputations or deaths at six months (22.6% against 36.2%), at the cost of more side effects; added to hydration before coronary angiography, it lowered contrast-induced kidney injury across 29 studies.
Mechanism of Action
Alprostadil is prostaglandin E1, a lipid, not a peptide. It relaxes smooth muscle and widens blood vessels wherever it is delivered (labels).
Erection by direct relaxation
Relaxes trabecular smooth muscle and dilates cavernosal arteries, trapping blood by compressing the venules (Caverject label).
Keeps the ductus open
In newborns, a continuous infusion keeps the ductus arteriosus open until heart surgery (Prostin VR label).
Cleared in the lungs
About 80% is metabolised in one pass through the lungs, so blood levels after a penile injection barely rise above the body's own (label).
Published Research
These are the trials in people, read from their PubMed abstracts, with dosing and safety from the Caverject label read on October 1, 2026.
Dose-response against placebo
In a dose-response study of 296 men with erectile dysfunction, every dose of intracavernosal alprostadil beat placebo, with a significant relation between dose and response (p ≤ 0.001) across 2.5 to 20 mcg. A separate dose-finding study of 201 men found the minimum effective dose was 2 mcg or less in 20 to 38% of men depending on the cause.
Injection beats the urethral pellet
In a randomised crossover trial in 111 men, 82.5% of intracavernosal injections produced an erection sufficient for intercourse against 53.0% of intraurethral doses, and 92.6% against 61.8% of men managed at least one. Mean doses were 26.1 mcg injected and 922.5 mcg intraurethrally.
The urethral pellet in practice
In 100 consecutive men treated with the intraurethral system at 125 to 1,000 mcg, 7% had well-sustained rigid erections and 30% full erections with partial rigidity, while 63% judged the result inadequate. Penile or perineal pain occurred in 24%, fainting in 3%, urethral bleeding in 3%, and one man needed drainage for priapism.
Six months of home use in diabetes
Thirty-one men with diabetes found an effective dose in 93.5% of cases, and over six months of self-injection 76.5% of injections were rated satisfactory by the patient. Sixteen of the 31 dropped out, three for lack of effect.
Newborns on low dose need not be ventilated
Of 300 newborns with suspected duct-dependent heart disease, apnoea was far more likely in unventilated infants at 15 ng/kg/min or more than below it (14 of 33 against 4 of 61); only 2 of 78 transported unventilated had apnoea in transit.
Lower doses keep the duct open
In 33 newborns with duct-dependent pulmonary circulation, a starting dose of about 20 ng/kg/min caused no apnoea needing intubation in 25 infants, and the duct stayed open on a maintenance dose of about 10.5 ng/kg/min.
Gut effects track the total dose
In 82 infants awaiting heart surgery, feeds were stopped more often as cumulative dose and duration rose; apnoea, fever and fast heart rate were linked to the maximum dose.
Caffeine to prevent apnoea
In a randomised trial of 51 newborns on PGE1, apnoea occurred in 20% given caffeine against 42% without it, a difference that was not statistically significant (p = 0.086).
Leg ulcers in arterial disease: no benefit
In 840 patients with Fontaine stage IV peripheral arterial disease, complete ulcer healing (18.4% against 17.2%) and major amputation (12.6% against 14.6%) did not differ from placebo.
Topical cream with PDE5 inhibitors
In men whose erectile dysfunction did not respond to tablets alone, adding topical alprostadil to a PDE5 inhibitor raised the IIEF-5 score from 12.4 to 17.1, while the tablet alone did not; adverse events were mild and no priapism occurred.
Psychogenic erectile dysfunction: injections against sex therapy
In a pilot trial of 50 men with psychogenic erectile dysfunction, 12 weeks of low-dose alprostadil self-injection (2.5-5.0 µg) restored unaided erections in 47% against 58% with sex therapy, a difference that was not significant, with similar intercourse frequency and satisfaction; erections lasted longer on injections (35 against 10 minutes).
Critical limb ischaemia: ulcers, pain and amputation
Pooling placebo-controlled trials (254 patients) in advanced peripheral arterial disease (stages III-IV) unsuitable for reconstruction, PGE1 improved ulcer healing or pain in 47.8% against 25.2% and cut major amputation or death at six months from 36.2% to 22.6%; adverse events were more frequent (39.6% against 15.4% in pooled groups).
Contrast kidney injury: 29 studies
Pooling 29 studies (5,623 patients) of coronary angiography, alprostadil 10 or 20 µg a day added to hydration lowered the incidence of contrast-induced nephropathy and kept creatinine, urea and cystatin C lower than hydration alone.
Dosing Data
For erectile dysfunction, Caverject is injected into the penis, starting at 2.5 mcg and titrated in the clinic; for newborns with duct-dependent heart disease, Prostin VR is a continuous intravenous infusion in intensive care.
Educational information, not medical advice. Each dose above is tagged with its source: an approved label, a published human study, animal data, or amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
Side Effects & Contraindications
Reported Side Effects
From the Caverject label (SPL version 19, effective May 13, 2024) and the trials above.
Contraindications & Cautions
From the label.
Legal Status
An approved drug in several forms.
Frequently Asked Questions
?Is alprostadil a peptide?
No. It is prostaglandin E1, a 20-carbon fatty acid. It is covered here because it is used and discussed alongside the peptides sold for sexual function.
?How well does it work?
In a 296-man dose-response study every dose beat placebo. Injected, it produced an erection sufficient for intercourse in 82.5% of attempts, against 53.0% for the urethral pellet.
?What is the starting dose?
The Caverject label starts at 2.5 mcg, or 1.25 mcg when the cause is purely neurogenic, with the first injections given in the clinic and the dose raised to the lowest that works.
?What is the main risk?
An erection that does not subside. The label warns about prolonged erection and priapism and says to seek medical help after four hours, and about penile fibrosis with repeated use.
?Why is it given to newborns?
Some heart defects leave a baby dependent on the ductus arteriosus, a fetal vessel that normally closes after birth. An alprostadil infusion keeps it open until surgery. Apnoea is the main risk, so it is given where ventilation is immediately available.
References
- [fda-pi] Caverject (alprostadil) prescribing information, sections 1, 2, 5 and 12.3 (DailyMed SPL version 19, effective May 13, 2024; read October 1, 2026).
- [pubmed] Linet OI, et al. "Efficacy and safety of intracavernosal alprostadil in men with erectile dysfunction. The Alprostadil Study Group." N Engl J Med, 1996;334(14):873-7. PMID: 8596569.
- [pubmed] Shabsigh R, et al. "Intracavernous alprostadil alfadex is more efficacious, better tolerated, and preferred over intraurethral alprostadil plus optional actis: a comparative, randomized, crossover, multicenter study." Urology, 2000;55(1):109-13. PMID: 10654905.
- [pubmed] Werthman P, et al. "MUSE therapy: preliminary clinical observations." Urology, 1997;50(5):809-11. PMID: 9372900.
- [pubmed] Tsai YS, et al. "Safety and efficacy of alprostadil sterile powder (S. Po., CAVERJECT) in diabetic patients with erectile dysfunction." Eur Urol, 2000;38(2):177-83. PMID: 10895010.
- [pubmed] Porst H. "The rationale for prostaglandin E1 in erectile failure: a survey of worldwide experience." J Urol, 1996;155(3):802-15. PMID: 8583582.
- [pubmed] Browning Carmo KA, et al. "Transporting newborn infants with suspected duct dependent congenital heart disease on low-dose prostaglandin E1 without routine mechanical ventilation." Arch Dis Child Fetal Neonatal Ed, 2007;92(2):F117-9. PMID: 16905574.
- [pubmed] Huang FK, et al. "Reappraisal of the prostaglandin E1 dose for early newborns with patent ductus arteriosus-dependent pulmonary circulation." Pediatr Neonatol, 2013;54(2):102-6. PMID: 23590954.
- [pubmed] Ofek Shlomai N, et al. "Cumulative Dose of Prostaglandin E1 Determines Gastrointestinal Adverse Effects in Term and Near-Term Neonates Awaiting Cardiac Surgery: A Retrospective Cohort Study." Children (Basel), 2023;10(9). PMID: 37761532.
- [pubmed] Salamati L, et al. "Caffeine Treatment for Prostaglandin E1-Induced Apnea Prevention in Congenital Heart Disease Neonates: A Randomized Clinical Trial." Crit Care Res Pract, 2025;2025:4923280. PMID: 40390868.
- [pubmed] Lawall H, et al. "Efficacy and Safety of Alprostadil in Patients with Peripheral Arterial Occlusive Disease Fontaine Stage IV: Results of a Placebo Controlled Randomised Multicentre Trial (ESPECIAL)." Eur J Vasc Endovasc Surg, 2017;53(4):559-566. PMID: 28189475.
- [pubmed] Garrido-Abad P, et al. "Combination therapy with topical alprostadil and phosphodiesterase-5 inhibitors after failure of oral therapy in patients with erectile dysfunction: a prospective, two-arm, open-label, non-randomized study." Int J Impot Res, 2022;34(2):164-171. PMID: 33483603.
- [pubmed] Creutzig A, et al. "Meta-analysis of randomised controlled prostaglandin E1 studies in peripheral arterial occlusive disease stages III and IV." Vasa, 2004;33(3):137-44. PMID: 15461065.
- [pubmed] Xu H, et al. "Efficacy of Alprostadil in Preventing Contrast-Induced Nephropathy: A Systematic Review and Meta-Analysis." Angiology, 2021;72(9):878-888. PMID: 33853365.
- [pubmed] Baum N, et al. "Prostaglandin E1 versus sex therapy in the management of psychogenic erectile dysfunction." Int J Impot Res, 2000;12(3):191-4. PMID: 11045914.
Sources & Citations
Studies were read from their PubMed abstracts; the Caverject Impulse label (DailyMed version 16, effective February 29, 2024) and the Prostin VR Pediatric label (DailyMed version 4, effective August 17, 2026) were read October 6, 2026.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Talk to a licensed clinician about your own situation.