Caverject Side Effects: What to Expect and When to Call Your Doctor

Caverject (alprostadil injection) is highly effective at producing erections, but it does come with a distinct side effect profile that every patient should understand before starting treatment. Most side effects are manageable, but a few require immediate medical attention. Here's a complete, honest breakdown of what you may experience — and when to call your doctor or go to the emergency room.

The Most Common Side Effect: Penile Pain

The single most common side effect of Caverject is penile pain at or after the injection site. This is reported in at least 10% of users in clinical trials — and some studies in real-world use suggest 20–40% of patients experience some degree of discomfort. The pain typically occurs during the erection and subsides as the erection resolves.

Pain level varies significantly between individuals. For many men it is mild; for others it is significant enough to discontinue therapy. If pain is a major problem, ask your urologist about switching to Trimix (which combines alprostadil with papaverine and phentolamine) — this typically requires a smaller dose volume and causes less pain.

Common Side Effects (Usually Manageable)

Penile pain: During or after the erection; typically mild to moderate

Bruising or bleeding at the injection site: More common in patients on blood thinners; compress the site for 5 minutes post-injection

Mild dizziness or lightheadedness: Due to the vasodilatory effect; typically brief and mild

Redness or swelling at the injection site: Usually resolves quickly; alternate injection sites to minimize

Prolonged erection (4 hours or less): Any erection lasting 1–4 hours is considered prolonged; uncomfortable but manageable

Serious Side Effects: When to Seek Immediate Medical Attention

Priapism — The #1 Medical Emergency

Priapism is a prolonged, painful erection that lasts more than 4 hours and is not associated with sexual arousal. This is a medical emergency. Without treatment, priapism can cause permanent damage to the erectile tissue and irreversible ED.

If you have an erection lasting more than 4 hours after using Caverject, go to the emergency room immediately. Do not wait.

In clinical studies with Caverject Sterile Powder, prolonged erection (4–6 hours) occurred in 4% of patients and priapism (>6 hours) occurred in less than 1% over 18 months. Risk is highest at the beginning of therapy or after a dose increase — which is why the first dose must be given in the physician's office.

Penile Fibrosis

With long-term use, repeated injections can cause scar tissue to form in the corpus cavernosum — a condition called penile fibrosis. This may cause the penis to curve (similar to Peyronie's disease), which can make intercourse difficult or painful. Your urologist should examine you periodically for signs of fibrosis. If you notice any new curvature or lumps, stop the medication and contact your provider.

Hypotension (Low Blood Pressure)

Intracavernosal alprostadil can increase peripheral blood levels of the drug and cause a drop in blood pressure. This is most relevant for men with preexisting cardiovascular conditions. Men for whom sexual activity is medically inadvisable due to cardiovascular risk should not use Caverject. Symptoms of hypotension include dizziness, lightheadedness, and fainting — report these to your doctor if they occur.

Needle Breakage

Though rare, needle breakage during injection has been reported. This is why proper injection technique — including careful needle handling and never reusing needles — is essential. Your provider will teach you the correct technique during your initial in-office visit.

Side Effects to Watch Long-Term

Penile fibrosis — new curvature, lumps, or hardness; stop medication and notify your provider

Reduced response over time — if doses needed for response are increasing, discuss with your urologist

Infection at injection site — redness, warmth, discharge; contact your provider promptly

Tips to Minimize Side Effects

Always use the lowest effective dose — never inject more than prescribed

Alternate injection sites between the left and right sides of the penis

Never inject more than 3 times per week or more than once in 24 hours

Compress the injection site for a few minutes after each injection

Keep all scheduled follow-up appointments with your urologist

For more safety information, read our guide on Caverject drug interactions: what to avoid and what to tell your doctor.

If you're having trouble finding alprostadil injection at your local pharmacy, medfinder can help you locate pharmacies near you that have it in stock.