HIV Glossary

As you’re learning about HIV, it’s important that you understand the commonly used words and phrases. Use this glossary to find definitions and explanations for things that are not familiar to you.

CD4 Cell/CD4 Cell Count — CD4 cells are also called T cells or T-helper cells. They are white blood cells that fight infection. A CD4 cell count is the number of CD4 cells in a sample of blood. HIV destroys CD4 cells. This can cause the CD4 cell count to go down.

Clinical Trial — A research study that uses human volunteers to answer specific health questions.

Dose — The recommended amount of a medicine to be taken.

Flare-Up — When a disease suddenly returns in a worse way than before.

Hepatitis B Virus (HBV) — The virus that causes hepatitis B, an inflammation of the liver that can lead to liver damage and liver cancer.

HIV (HIV-1) — HIV—Human immunodeficiency virus, the virus that causes AIDS. HIV-1—The HIV type responsible for the majority of HIV infections worldwide.

Immune System — The body's defense system to fight off infections and other diseases. Cells of your immune system are attacked and destroyed by HIV.

Lactic Acidosis — A condition caused by a build-up of a waste product called lactate in the blood. Symptoms may include stomach problems (nausea and vomiting), breathing or muscle problems, and general weakness. Severe, untreated lactic acidosis can be life-threatening.

Prescribing Information — Also referred to as the package insert, product label, or product information, this document is the primary reference for information about a prescription drug. The Prescribing Information also includes the Medication Guide, which provides important information about the prescription drug like how to take it and how to store it. Both the Prescribing Information and Medication Guide are approved by the U.S. Food and Drug Administration.

Regimen — Refers to the combination of medicines you take to treat your HIV infection.

Resistance — When HIV mutates (or changes form), resulting in a virus that cannot be controlled with certain HIV medicines.

Undetectable Viral Load — is when the amount of HIV in the blood is too low to be detected by a test. HIV medicines may reduce a person's viral load to an undetectable level; however, that does not mean the person is cured. Some HIV remains inside cells and in body tissues. The person still has HIV and needs to stay on HIV medicines. Having and keeping an undetectable viral load reduces the chances of passing HIV on to others.

Viral Load — The amount of HIV in a sample of blood, as measured by a lab test. If a viral load is undetectable, it means that the amount of HIV in the blood is below the limit of detection of the lab test. Healthcare providers use viral load test results to monitor HIV.

Please see the full Prescribing Information including Medication Guide with important warnings

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What is TRUVADA?

TRUVADA (emtricitabine 200 mg and tenofovir disoproxil fumarate 300 mg) is a prescription medicine used with other HIV-1 medicines to treat HIV-1 infection in people who weigh at least 35 kg (77 lbs).

TRUVADA does not cure HIV-1 infection or AIDS. To control HIV-1 infection and decrease HIV-1 related illnesses, you must keep taking TRUVADA. Ask your healthcare provider if you have questions about how to prevent passing HIV-1 to others. Always practice safer sex and use condoms to lower the chance of sexual contact with body fluids. Never reuse or share needles or other items that have body fluids on them.


What is the most important information I should know about TRUVADA?

TRUVADA can cause serious side effects:

  • Too much lactic acid in your blood (lactic acidosis), which is a serious medical emergency. Symptoms of lactic acidosis include weakness or being more tired than usual, unusual muscle pain, being short of breath or fast breathing, nausea, vomiting, stomach-area pain, cold or blue hands and feet, feeling dizzy or lightheaded, and/or fast or abnormal heartbeats.
  • Serious liver problems. Your liver may become large and tender, and you may develop fat in your liver. Symptoms of liver problems include your skin or the white part of your eyes turns yellow, dark “tea-colored” urine, light-colored stools, loss of appetite for several days or longer, nausea, and/or stomach-area pain.
  • You may be more likely to get lactic acidosis or serious liver problems if you are female, very overweight (obese), or have been taking TRUVADA for a long time. In some cases, these serious conditions have led to death. Call your healthcare provider right away if you have any symptoms of these conditions.
  • Worsening of hepatitis B (HBV) infection. If you also have HBV and stop taking TRUVADA, your hepatitis may suddenly get worse. Do not stop taking TRUVADA without first talking to your healthcare provider, as they will need to monitor your health. TRUVADA is not approved for the treatment of HBV.

Who should not take TRUVADA?

Do not take TRUVADA if you also take a medicine that contains: emtricitabine, tenofovir alafenamide, or tenofovir disoproxil fumarate (ATRIPLA, COMPLERA, EMTRIVA, DESCOVY, GENVOYA, ODEFSEY, STRIBILD, VIREAD); lamivudine (Combivir, Dutrebis, Epivir, Epivir-HBV, Epzicom, Triumeq, Trizivir); or adefovir (HEPSERA).

What are the other possible side effects of TRUVADA?

Serious side effects of TRUVADA may also include:

  • Kidney problems, including kidney failure. Your healthcare provider may do blood tests to check your kidneys before and during treatment with TRUVADA. If you develop kidney problems, your healthcare provider may tell you to take TRUVADA less often, or to stop taking TRUVADA.
  • Bone problems, including bone pain or bones getting soft or thin, which may lead to fractures. Your healthcare provider may do tests to check your bones.
  • Changes in body fat, which can happen in people taking HIV-1 medicines.
  • Changes in your immune system. Your immune system may get stronger and begin to fight infections. This may cause minor symptoms such as fever, but can also lead to serious problems. Tell your healthcare provider if you have any new symptoms after you start taking TRUVADA.

The most common side effects of TRUVADA in people taking TRUVADA to treat HIV-1 infection include diarrhea, nausea, tiredness, headache, dizziness, depression, problems sleeping, abnormal dreams, and rash. Tell your healthcare provider if you have any side effects that bother you or do not go away.

What should I tell my healthcare provider before taking TRUVADA?

  • All your health problems. Be sure to tell your healthcare provider if you have or have had any kidney, bone, or liver problems, including hepatitis virus infection.
  • If you are pregnant or plan to become pregnant. It is not known if TRUVADA can harm your unborn baby. Tell your healthcare provider if you become pregnant while taking TRUVADA.
    Pregnancy Registry: A pregnancy registry collects information about your health and the health of your baby. There is a pregnancy registry for women who take medicines to treat HIV-1 during pregnancy. For more information about the registry and how it works, talk to your healthcare provider.
  • If you are breastfeeding (nursing) or plan to breastfeed. Do not breastfeed. HIV-1 can be passed to the baby in breast milk.
  • All the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements. TRUVADA may interact with other medicines. Keep a list of all your medicines and show it to your healthcare provider and pharmacist when you get a new medicine.
  • If you take certain other medicines with TRUVADA, your healthcare provider may need to check you more often or change your dose. These medicines include: didanosine (Videx EC), atazanavir (Reyataz), atazanavir with cobicistat (Evotaz), darunavir (Prezista), darunavir with cobicistat (Prezcobix), lopinavir with ritonavir (Kaletra), or ledipasvir with sofosbuvir (HARVONI).

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit, or call 1-800-FDA-1088.

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