You may feel drowsy or dizzy. Do not drive, use machinery, or do anything that requires mental alertness until you know how prazosin affects you. To reduce the risk of dizzy or fainting spells, do not sit or stand up quickly. Avoid alcoholic drinks; they can make you more drowsy, and can increase flushing and rapid heartbeats. Taking initial doses of prazosin at bedtime can lessen the effects of drowsiness and dizziness, but be careful if you have to get up during the night. Drowsiness and dizziness are more likely to occur after the first dose, after an increase in dose, or during hot weather or exercise. These effects can decrease once your body adjusts to this medicine.
Although extremely rare in men taking prazosin, contact you health care provider immediately if you experience prolonged and painful erection of the penis which is unrelated to sexual activity (priapism). If not brought to immediate medical attention, priapism can lead to permanent erectile dysfunction (impotence).
Your mouth may get dry. Chewing sugarless gum or sucking hard candy, and drinking plenty of water, will help.
Do not take nonprescription medicine for weight-loss without asking your prescriber or health care professional. Also, do not take cough and cold, hay fever or sinus medications without asking your prescriber or health care professional.
If you are going to have surgery, tell your prescriber or health care professional that you are taking prazosin.
What side effects may I notice from this medicine?
Side effects that you should report to your prescriber or health care professional as soon as possible:
difficulty breathing, shortness of breath
prolonged painful erection of the penis (priapism)
blurred vision
fainting spells, lightheadedness
irregular heartbeat, palpitations or chest pain
mental depression
swelling of the legs and ankles
vomiting
Side effects that usually do not require medical attention (report to your prescriber or health care professional if they continue or are bothersome):
constipation or diarrhea
drowsiness or dizziness
dry mouth
headache
nausea
sexual difficulties (impotence)
stomach pain
unusual weakness or tiredness
