Short answer: Caverject (alprostadil) is injected into the side of the penis, with the first doses set in the prescriber's office; an erection is expected in 5 to 20 minutes.1 Cialis (tadalafil) is a tablet taken at least 30 minutes before sex, or once daily, and is also approved for an enlarged prostate.2 Neither has a boxed warning, and neither label compares the two.
| Caverject | Cialis | |
|---|---|---|
| Drug | Alprostadil, injected into the penis1 | Tadalafil, a PDE5 inhibitor tablet2 |
| Approved for | Erectile dysfunction, and as an aid in diagnosing it1 | Erectile dysfunction, enlarged prostate (BPH), or both2 |
| Starting dose | 2.5 mcg in the office (1.25 mcg for nerve-related ED), stepped up to the lowest dose that works1 | As needed: 10 mg; once daily: 2.5 mg2 |
| Limits | Not above 60 mcg; at home no more than 3 times a week, at least 24 hours apart1 | As needed: up to 20 mg, at most once a day in most men; daily: up to 5 mg2 |
| Timing | Erection in 5 to 20 minutes, lasting no longer than 1 hour1 | At least 30 minutes before sex; works for up to 36 hours in most men2 |
| Most common side effects | Penile pain 37%; prolonged erection 4%; penile scarring 3%1 | Headache 11% to 15% vs 5% on placebo; indigestion 4% to 10% vs 1%2 |
| Not used with | Conditions that make priapism more likely, penile deformity such as Peyronie's disease, or a penile implant1 | Nitrates in any form, or riociguat2 |
| Boxed warning | None1 | None2 |
Both labels say an erection lasting more than 4 hours needs emergency care. With Caverject it happened in 4% (priapism over 6 hours in 0.4%); the Cialis label calls it rare.12 Caverject's other warnings are local: scarring inside the penis, bleeding at the site with blood thinners, low blood pressure and broken needles.1 Cialis can sharply drop blood pressure with nitrates, adds to alpha-blockers, and its label lists sudden vision or hearing loss and lower doses with kidney or liver problems.2 These numbers come from separate trials with different people, lengths and methods, so they are not a head-to-head comparison.
The Cialis label says it has not been studied with other ED treatments, and the Caverject label says combining it with other penile injections has not been studied.21 Which, if either, fits is for your prescriber. More detail: Caverject side effects, Cialis side effects, the Caverject and Cialis dosing schedules, the Cialis missed-dose page, the alprostadil and tadalafil guides, and Caverject vs Edex: how do the two alprostadil injections differ?.