What medication can cause urinary retention (difficulty peeing) as a side effect?

Many types: There are many types of medications that can potentiate retention. The most common are decongestants such as Sudafed, which can increase urinary sphincter tone. Antihistamines, taken for allergies, may cause less bladder contractility. Anticholinergic preparations, taken for overactive bladder symptoms (urgency/frequency) can also make it more difficult to empty the bladder.