Efavirenz comes as a capsule and as a tablet to take by mouth with plenty of water on an empty stomach once a day. To help you remember to take efavirenz, take it around the same time every day. Taking efavirenz at bedtime may make side effects less bothersome. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take efavirenz exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Efavirenz controls HIV infection, but does not cure it. Continue to take efavirenz even if you feel well. Do not stop taking efavirenz without talking to your doctor. If you miss doses or stop taking efavirenz, your condition may become more difficult to treat.

Efavirenz may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

upset stomach
vomiting
stomach pain
diarrhea
indigestion
dizziness
headache
difficulty concentrating
confusion
forgetfulness
strange thoughts
abnormally happy mood
difficulty falling asleep or staying asleep
unusual dreams
pain
increased sweating
cough
Some side effects can be serious. The following symptoms are uncommon, but if you experience any of them, call your doctor immediately:

rash
itching
blisters or sores on skin
peeling skin
itching
fever
fainting
nervousness
aggressive or angry behavior
depression
thoughts of hurting yourself
seeing things or hearing voices that do not exist (hallucinating)
extreme tiredness
lack of energy
loss of appetite
pain in the upper right part of the stomach
unusual bleeding or bruising
yellowing of the skin or eyes
flu-like symptoms
Efavirenz may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.

Talk to your doctor about drinking grapefruit juice while taking this medicine.

In case of overdose, call your local poison control center at 1-800-222-1222. If the victim has collapsed or is not breathing, call local emergency services at 911.

Symptoms of overdose may include:

movements of your body that you cannot control
dizziness
headache
difficulty concentrating
nervousness
confusion
forgetfulness
difficulty falling asleep or staying asleep
unusual dreams
drowsiness
seeing things or hearing voices that do not exist (hallucinating)
abnormally happy mood
strange thoughts

Keep all appointments with your doctor and the laboratory. Your doctor may order certain lab tests to check your body's response to efavirenz.

Before having any laboratory test, tell your doctor and the laboratory personnel that you are taking efavirenz.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

Take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

Efavirenz is used with other medications to treat human immunodeficiency virus (HIV) infection in patients with or without acquired immunodeficiency syndrome (AIDS). Efavirenz is in a class of medications called nonnucleoside reverse transcriptase inhibitors (NNRTIs). Efavirenz works by slowing the spread of HIV in the body. Efavirenz does not cure HIV infection and may not prevent you from developing HIV-related illnesses. Efavirenz does not prevent you from spreading HIV to other people.

Efavirenz is also used with another medication to help prevent infection in health care workers or other people who were accidentally exposed to HIV. Talk to your doctor about the possible risks of using this medication for your condition. This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom). Throw away any medication that is outdated or no longer needed. Talk to your pharmacist about the proper disposal of your medication.

Before taking efavirenz,

tell your doctor and pharmacist if you are allergic to efavirenz or any other medications.
do not take astemizole (Hismanal); cisapride (Propulsid); ergot-type medications such as bromocriptine (Parlodel), cabergoline (Dostinex), dihydroergotamine (D.H.E. 45, Migranal), ergoloid mesylates (Germinal, Hydergine), ergonovine (Ergotrate), ergotamine (Bellergal-S, Cafergot, Ergomar, Wigraine), methylergonovine (Methergine), methysergide (Sansert), and pergolide (Permax); or triazolam (Halcion) while taking efavirenz.
tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, and nutritional supplements you are taking. Be sure to mention any of the following: acetaminophen (Tylenol, others); anticoagulants ('blood thinners') such as warfarin (Coumadin); antidepressants; antifungals such as itraconazole (Sporanox), and ketoconazole (Nizoral); calcium channel blockers such as amlodipine (Norvasc), diltiazem (Cardizem, Dilacor, Tiazac, others), felodipine (Lexxel, Plendil), nifedipine (Adalat, Procardia), nisoldipine (Sular), and verapamil (Calan, Covera, Isoptin, Verelan); chlorpheniramine in over-the-counter cold products; cholesterol-lowering medications (statins); cimetidine (Tagamet); clarithromycin (Biaxin, Prevpac); danazol (Danocrine); dexamethasone (Decadron); erythromycin (E.E.S., E-Mycin, Erythrocin); iron products; isoniazid (INH, Nydrazid); medications for anxiety, mental illness, or pain; medications for HIV or AIDS such as amprenavir (Agenerase), indinavir (Crixivan), ritonavir (Norvir) and saquinavir (Fortovase); medications for seizures such as carbamazepine (Tegretol), phenobarbital, and phenytoin (Dilantin, Phenytek); methotrexate (Rheumatrex); methadone (Dolophine); metronidazole (Flagyl); niacin (nicotinic acid); nonsteroidal anti-inflammatory medications (NSAIDs) such as celecoxib (Celebrex), diclofenac (Voltaren), ibuprofen (Advil, Motrin), naproxen (Aleve, Anaprox, Naprosyn), and piroxicam (Feldene); oral contraceptives (birth control pills); oral medications for diabetes such as glipizide (Glucotrol, Metaglip) and tolbutamide (Orinase); proton pump inhibitors such as lansoprazole (Prevacid), omeprazole (Prilosec), and pantoprazole (Protonix); quinidine (Quinidex); quinine; rifabutin (Mycobutin); rifampin (Rifadin, Rimactane); sedatives; sildenafil (Viagra);sleeping pills; sulfamethoxazole (Bactrim, Septra); tamoxifen (Nolvadex); torsemide (Demadex); tranquilizers; troleandomycin (TAO); or zafirlukast (Accolate). Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
tell your doctor what herbal products you are taking, especially products that contain kava or St. John's wort.
tell your doctor if you drink or have ever drunk large amounts of alcohol; if you use or have ever used street drugs or have overused prescription medications; if you have or have ever had seizures, high cholesterol, or mental illness; or if you have or have ever had heart, liver, or pancreas disease.
you should not become pregnant while taking efavirenz. You will have to have a negative pregnancy test before you begin taking this medication and use two approved forms of birth control while you are taking it. If you become pregnant while taking efavirenz, call your doctor. You should not breastfeed if you are infected with HIV or are taking efavirenz.
if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking efavirenz.
you should know that efavirenz may make you drowsy, dizzy, or unable to concentrate. Do not drive a car or operate machinery until you know how this medication affects you.
ask your doctor about the safe use of alcoholic beverages while you are taking efavirenz. Alcohol can make the side effects from efavirenz worse.
you should know that your body fat may increase or move to different areas of your body such as your breasts and upper back.