You have chronic hepatitis B when the virus is active in your body for more than 6 months. The virus can damage liver cells and cause your liver to become swollen and tender.

Most people who have chronic hepatitis B don't have symptoms. But they can still pass the infection to other people, especially the people they live with or have sex with, unless they receive treatment that gets rid of the virus.

Most people with chronic hepatitis B don't develop serious problems. But about 15 to 25 people out of 100 who have the infection will die of cirrhosis or liver cancer.^{footnote 1} When there is a lot of the virus in your body, your chance of having these problems is greater. Sometimes, chronic hepatitis B can lead to severe liver damage. If this happens, you may need a liver transplant.

There are several antiviral medicines that can be used to treat chronic hepatitis B. They are sorted into two groups:

• Interferons, such as interferon alfa-2b and peginterferon alfa-2a. Interferons are given as a shot 1 to 3 times a week for 4 to 12 months.
• Nucleoside reverse transcriptase inhibitors (NRTIs) such as adefovir, entecavir, lamivudine, telbivudine, and tenofovir. NRTIs are taken as a pill once a day for at least a year, and usually for many years.

When you take interferons, you are less likely to relapse after you stop taking the medicine than if you took NRTIs. But fewer people are helped by interferons than by NRTIs.^{footnote 2}

Experts recommend antiviral medicines if you have high levels of both the hepatitis B virus and liver enzymes in your blood for at least 6 months or if you have liver disease.

But antiviral medicines may not be right for everyone. The medicines can be helpful if you have or are likely to get liver damage, such as cirrhosis. But they may not help if you already have severe liver damage. People who have had an organ transplant or who drink too much alcohol or use illegal drugs may not be able to take some of these medicines.

You may not need to take antiviral medicines if you have normal or only slightly higher-than-normal levels of liver enzymes in your blood and if your liver isn't damaged. Your doctor may remove a tiny piece (biopsy) of your liver to see if it has been affected by the virus.

Results from your blood tests can help you and your doctor decide which treatment might work best for you or if you need to take any medicine at all. Some people with chronic hepatitis B can live active, full lives by taking good care of themselves and getting regular checkups to watch for liver problems. Others may not need medicine right away, but will start taking antivirals later if tests show that the virus is active.

Antiviral medicines can stop or slow the growth of the hepatitis B virus and help prevent serious liver problems.

Interferon stops the growth of the hepatitis B virus over the long term in about 35 out of 100 people.^{footnote 2} This means that it doesn't stop the virus in about 65 out of 100 people. Recent studies suggest that peginterferon works a little better than interferon.^{footnote 3, footnote 4}

NRTIs slow the growth of the hepatitis B virus in your body. Studies show that lamivudine and adefovir can reduce liver damage in about half of the people who take these medicines.^{footnote 5, footnote 6} Entecavir can greatly reduce liver swelling and scarring. Tenofovir is effective at reducing the amount of hepatitis B virus in the body.^{footnote 7} Some studies show that entecavir works better than lamivudine or adefovir.^{footnote 8, footnote 9, footnote 10} Tenofovir works better than adefovir against hepatitis B virus that is resistant to lamivudine.^{footnote 11}

Antiviral medicines can have serious side effects that may cause problems throughout your treatment. Some people are not bothered by the side effects, while others stop taking their medicines because they feel too sick to finish them.

If you take interferons, you're more likely to have side effects than if you take NRTIs.

Side effects of interferons include:

• Fever.
• Headaches.
• Hair loss.
• Depression, which can be severe.

In rare cases, interferons can cause confusion and might affect your heart, thyroid, or kidneys.

Side effects of NRTIs may include:

• Fever.
• Sore throat.
• Diarrhea.
• Headaches.
• Fatigue.
• Weakness.
• Dizziness.
• Stomach or back pain.

In rare cases, NRTIs have caused severe liver problems or a buildup of acid in the blood.

After any kind of treatment for hepatitis B, there is a chance that the virus will come back after you've stopped treatment.

The virus may also become resistant to the drug that you're taking. This means that the medicine no longer works to stop or slow the virus. If this happens, you may have to try another medicine. Drug resistance is more likely with some NRTIs.

Your doctor might recommend antiviral medicines if:

• You have hepatitis B antigens in your blood.
• You have high levels of the virus in your blood.
• Your liver enzymes are more than twice the normal amount.
• You have liver disease.