Alprostadil (Caverject, MUSE, Vitaros)

What alprostadil is and how it works

Alprostadil is chemically identical to prostaglandin E1, a tissue hormone produced by the body. Among its most important effects are the dilation of blood vessels and the inhibition of platelets. For erectile dysfunction it is applied where it is meant to act: as an injection directly into the corpus cavernosum (Caverject), as a small pellet inserted into the urethra (MUSE), or as a cream on the tip of the penis (Vitaros).

According to the summary of product characteristics, alprostadil relaxes the smooth muscle of the cavernous trabeculae and dilates the cavernous arteries. The cavities fill with blood and press the draining veins against the firm sheath of the corpus cavernosum, so the blood is trapped. After an injection, the erection usually begins after 5 to 15 minutes; its duration depends on the dose. PDE5 inhibitors such as sildenafil, tadalafil or vardenafil, by contrast, prolong the signal of the messenger substance cGMP that arises during sexual arousal. Alprostadil is therefore considered an alternative when tablets do not work sufficiently (Papadopoulos 2025).

What the studies show

Injection into the corpus cavernosum: the approval studies

Linet and Ogrinc 1996 (NEJM) report three studies in men with erectile dysfunction of vascular, neurogenic, psychogenic and mixed causes. In the dose-response study with 296 men, every dose was superior to placebo, and higher doses worked more often. In the dose-finding study with 201 men, a very low dose was already sufficient in 20 to 38 percent, depending on the cause. In the 6-month self-injection study with 683 men, sexual activity was possible after 94 percent of injections; the men rated it as satisfactory after 87 percent, their female partners after 86 percent.

Long-term self-injection in Europe

The European Alprostadil Study Group enrolled 848 men aged 18 to 75. In 93 percent, a dose for use at home could be found in the doctor’s office; in 86 percent it was at most 20 micrograms. Over 6 months, 88 percent of injections led to satisfactory sexual activity according to the men and 90 percent according to their female partners. Only 3 percent discontinued because of pain.

Urethral form (MUSE)

Padma-Nathan 1997 (NEJM) first tested 1,511 men aged 27 to 88 with organic erectile dysfunction in the doctor’s office; 65.9 percent achieved an erection sufficient for intercourse. These men were then assigned to alprostadil or placebo at home for three months: 64.9 percent under alprostadil had successful intercourse at least once, compared with 18.6 percent under placebo. In men who responded, on average 7 out of 10 applications were followed by intercourse, regardless of age and cause, including in diabetes and after surgery.

Cream (Vitaros)

Padma-Nathan and Yeager 2006 jointly analyzed two placebo-controlled studies with 1,732 men over 12 weeks; men with diabetes or on nitrates were also included. The erectile function score changed by +1.6 to +2.5 points compared with −0.7 under placebo. A 2025 meta-analysis with 5,869 patients found +4.7 points compared with placebo for the cream and also a clear improvement for the urethral form, but rates the study quality as low (Papadopoulos 2025).

What users report

A questionnaire study asked 42 men about their long-term experience with self-injection. 57 percent were still using it after an average of just under 4 years; 43 percent had stopped after an average of 21 months; no serious complications were reported (Lundberg 1996).

Where the data stop

• Age of the studies. The large studies on the injection and the urethral form date from the 1990s; direct comparisons with PDE5 inhibitors in large modern studies are lacking.
• Quality for cream and urethral form. The 2025 meta-analysis rates the methodological quality of the studies as low, and the results vary widely.
• Very long-term use. Data over many years come mainly from small observations, such as a survey of 42 men.
• Size of the cream’s effect. In the large analysis, the advantage over placebo was a few points on the erectile function score.

Status, approval and legal

Alprostadil is prescription-only in Germany. Approved for erectile dysfunction are Caverject for injection into the corpus cavernosum (since July 30, 1997), MUSE for urethral use (since February 22, 1999) and Vitaros cream with 300 micrograms (since March 9, 2016).

The approved use according to the summary of product characteristics: with Caverject, the first injections and the adjustment to the lowest effective dose are carried out in the doctor’s office; the erection should not last longer than one hour. Most patients respond to 5 to 20 micrograms; at most 40 micrograms are approved, at most once a day and not more often than three times a week. For MUSE, at most 2 applications in 24 hours and 7 in 7 days apply; for Vitaros, at most 2 to 3 applications per week and one in 24 hours.

Safety

The most common side effect of the injection is penile pain: according to the summary of product characteristics, it occurred at least once in 30 percent of patients and after 11 percent of injections, mostly mild to moderate; 3 percent discontinued because of it. Penile fibrosis, that is, scarring with nodules or curvature, was found in 3 percent of study participants, and in about 8 percent in longer studies; the risk may increase with the duration of treatment. An erection of 4 to 6 hours occurred in 4 percent, priapism of more than 6 hours in 0.4 percent. Priapism is an emergency; treatment must begin within 6 hours at most. In the approval studies, bruising occurred in addition in 8 percent of men (Linet and Ogrinc 1996).

With the urethral form, mild penile pain after 10.8 percent of applications was the most common side effect; in the doctor’s office, blood pressure dropped in 3.3 percent, and priapism or fibrosis did not occur in the study (Padma-Nathan 1997). With the cream, most side effects were limited to the application site and subsided within 2 hours (Padma-Nathan and Yeager 2006).

Sources

• Linet OI, Ogrinc FG, N Engl J Med 1996 – injection into the corpus cavernosum: three studies with 296, 201 and 683 men
• European Alprostadil Study Group, Br J Urol 1998 – long-term safety of self-injection, 848 men
• Padma-Nathan H et al., N Engl J Med 1997 – transurethral alprostadil (MUSE), RCT with 1,511 men
• Padma-Nathan H, Yeager JL, Urology 2006 – alprostadil cream, pooled analysis of two RCTs with 1,732 patients
• Papadopoulos I et al., Andrology 2025 – meta-analysis on cream and urethral form, 5,869 patients
• Lundberg L et al., Scand J Urol Nephrol 1996 – long-term experience with self-injection, questionnaire in 42 patients
• Summary of product characteristics Caverject 10 µg/20 µg, as of 11/2023 – dosage, mode of action, priapism, fibrosis
• Summary of product characteristics MUSE 250/500/1000 µg, as of 01/2026 – indication and maximum use
• Summary of product characteristics Vitaros 300 micrograms/100 mg cream, as of 05/2022 – indication and frequency of use
• German Ordinance on Prescription-Only Medicines (AMVV), Annex 1 – prescription requirement