Before taking perphenazine, tell your doctor or pharmacist if you are allergic to it, or to other phenothiazines (such as chlorpromazine, fluphenazine), 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: decreased bone marrow function, serious head injury, liver problems, nervous system problem (such as drug/alcohol overdose), Parkinson's disease, history of alcohol/substance abuse, low blood pressure, breathing problems (such as asthma, emphysema), breast cancer, fast/irregular heartbeat, heart valve problems, a certain adrenal gland tumor (pheochromocytoma), restless legs syndrome, seizure disorder, a certain severe reaction to other medications (neuroleptic malignant syndrome), difficulty urinating (such as due to prostate problems).

Perphenazine may cause a condition that affects the heart rhythm (QT prolongation). QT prolongation can rarely cause serious (rarely fatal) fast/irregular heartbeat and other symptoms (such as severe dizziness, fainting) that need medical attention right away.

The risk of QT prolongation may be increased if you have certain medical conditions or are taking other drugs that may cause QT prolongation. Before using perphenazine, tell your doctor or pharmacist of all the drugs you take and if you have any of the following conditions: certain heart problems (heart failure, slow heartbeat, QT prolongation in the EKG), family history of certain heart problems (QT prolongation in the EKG, sudden cardiac death).

Low levels of potassium or magnesium in the blood may also increase your risk of QT prolongation. This risk may increase if you use certain drugs (such as diuretics "water pills") or if you have conditions such as severe sweating, diarrhea, or vomiting. Talk to your doctor about using perphenazine safely.

This drug may make you dizzy or drowsy or blur your vision. Alcohol or marijuana (cannabis) can make you more dizzy or drowsy. Do not drive, use machinery, or do anything that needs alertness or clear vision until you can do it safely. Avoid alcoholic beverages. Talk to your doctor if you are using marijuana (cannabis).

This medication may make you more sensitive to the sun. Limit your time in the sun. Avoid tanning booths and sunlamps. Use sunscreen and wear protective clothing when outdoors. Tell your doctor right away if you get sunburned or have skin blisters/redness.

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

Caution is advised during hot weather because perphenazine can reduce sweating, increasing your risk for a severe reaction to too much heat (heatstroke). Drink plenty of fluids. Avoid strenuous exercise in hot weather. If you become overheated, promptly seek cooler shelter and/or stop exercising. Get medical help right away if your body temperature is above normal or if you have mental/mood changes, headache, or dizziness.

Children may be more sensitive to the side effects of this drug, especially uncontrolled movements.

Older adults may be more sensitive to the side effects of this drug, especially dizziness, lightheadedness, drowsiness, muscle spasm/stiffness, tardive dyskinesia, and QT prolongation (see above). Drowsiness, dizziness, and lightheadedness can increase the risk of falling.

During pregnancy, this medication should be used only when clearly needed. Babies born to mothers who have used this drug during the last 3 months of pregnancy may rarely develop symptoms including muscle stiffness or shakiness, drowsiness, feeding/breathing difficulties, or constant crying. If you notice any of these symptoms in your newborn especially during their first month, tell the doctor right away.

Since untreated mental/mood problems (such as schizophrenia, bipolar disorder, schizoaffective disorder) can be a serious condition, do not stop taking this medication unless directed by your doctor. If you are planning pregnancy, become pregnant, or think you may be pregnant, immediately discuss with your doctor the benefits and risks of using this medication during pregnancy.

Perphenazine passes into breast milk and may have undesirable effects on a nursing infant. Consult your doctor before breastfeeding.