Before taking terazosin, tell your doctor or pharmacist if you are allergic to it; or to other alpha blockers such as doxazosin or prazosin; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: low blood pressure/fainting, certain eye problems (cataracts, glaucoma).

This drug may make you dizzy or drowsy. Alcohol or marijuana (cannabis) can make you more dizzy or drowsy. Do not drive, use machinery, or do anything that needs alertness until you can do it safely. You should avoid driving or hazardous tasks for 12 hours after the first dose, after your dose is increased, and when this medication is restarted after it has been stopped. Limit alcoholic beverages. Talk to your doctor if you are using marijuana (cannabis).

Before having surgery (including cataract/glaucoma eye surgery), tell your doctor or dentist if you are taking or have ever taken this medication, and about all the other products you use (including prescription drugs, nonprescription drugs, and herbal products).

Older adults may be more sensitive to the side effects of this drug, especially dizziness, fainting, and low blood pressure when getting up from a sitting or lying position. These side effects can increase the risk of falling.

During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.

It is unknown if this drug passes into breast milk. Consult your doctor before breastfeeding.