A large study of nearly 74,000 men suggests that long-term use of tadalafil, best known as Cialis, may be linked to a higher risk of glaucoma and other eye pressure problems. Men prescribed the drug for urinary symptoms caused by an enlarged prostate were 22% more likely to develop glaucoma, 32% more likely to develop ocular hypertension, and 33% more likely to be diagnosed with primary open-angle glaucoma or start glaucoma treatment over five years.