A large study of 2102 men from 11 different multicentered, randomized, double-blind, placebo controlled trials of tadalafil reported the drug is well tolerated overall. Fifty-one percent of men using tadalafil 20 mg had at least one adverse event (AE), but only 3.2% discontinued treatment. The most common AEs reported with the 20 mg dose were headache (15%), dyspepsia (8%), and back pain (5%) (Table 1). Most AEs are a result of vasodilation of vascular beds other than in the penis.

Table 1. Most common tadalafil treatment-emergent adverse events.

Safety variable	Placebo (n = 638)	Tadalafil 10 mg (n = 321)	Tadalafil 20 mg (n = 1143)
Subjects with ≥1 treatment emergent AE	247 (39%)	185 (58%)	577 (51%)
Discontinuation for AE	8 (1.3%)	5 (1.6%)	36 (3.2%)
Most common treatment emergent AEs
Headache	30 (5%)	38 (12%)	173 (15%)
Dyspepsia	7 (1%)	23 (7%)	90 (8%)
Back pain	15 (2%)	20 (6%)	60 (5%)
Nasopharyngitis	24 (4%)	26 (8%)	23 (2%)
Myalgia	6 (1%)	16 (5%)	33 (3%)
Flushing	8 (1%)	10 (3%)	39 (3%)
Nasal congestion	4 (1%)	11 (3%)	28 (2%)
Pain in limb	5 (1%)	10 (3%)	31 (3%)

Although frequently asked about by patients, priapism is rarely associated with PDE5 inhibitors. Several case reports have found an extraordinarily uncommon link between sildenafil and priapism, and only a single case report exists in the literature implicating tadalafil with priapism. PDE5 inhibitors including tadalafil may actually have some benefit in preventing recurrent, or stuttering, priapism. A small series of 4 men with stuttering priapism were administered daily PDE5 inhibitors, one case of which used tadalafil, and all four men had decreases in priapism recurrences.