Harvoni is a new medication for hepatitis C. It’s a single tablet taken once per day that contains two drugs: ledipasvir and sofosbuvir. When taken for 12 weeks, Harvoni cures most cases of hepatitis C.

Previous drug treatments for hepatitis C took longer and had lower cure rates. On average, treatment took two to four months with a cure rate of 50 to 80 percent. Harvoni cures 93 to 100 percent of patients in just 12 weeks.

Harvoni causes few side effects compared with previous drugs. But because Harvoni is so new, we’re still learning about its side effects. The following are the main side effects we know about today.

Central nervous system

One of the main side effects of Harvoni is tiredness. This tends to increase the longer you take the drug. Tiredness may be related to an interaction with other drugs that can slow your heart rate. If you feel tired while taking Harvoni, talk with your doctor about how you can increase your energy level.

Some people have headaches when they take Harvoni. This side effect generally gets worse the longer you take the drug. If you have headaches during your Harvoni treatment, ask your doctor about ways to increase your comfort.

For a small number of people, Harvoni causes insomnia (trouble sleeping). This side effect also may get worse the longer you take the drug. Your doctor can suggest ways to improve your sleep if you have problems while taking Harvoni.

Recently, warnings about mood changes like irritability or depression were added to the drug label. These effects may be linked to sofosbuvir, one of the drugs in the Harvoni tablet. Some patients have reported that taking sofosbuvir with other hepatitis C treatments caused them to feel irritable, depressed, or suicidal. These effects are more likely to occur if a patient has a history of depression or other mental illness.

If you have mood changes or become depressed while taking Harvoni, call your doctor right away.

Digestive system

Like many drugs, Harvoni can cause some stomach problems. A small number of patients have reported nausea and diarrhea while taking the drug. Like some other side effects, these tend to get a little worse the longer you take the drug. If you have these side effects, your doctor may suggest some over-the-counter treatments that can help.

If you have reduced liver function, you should still be able to take the normal dosage of Harvoni. Before taking Harvoni, be sure to share all of your medical records with your doctor, including information on your liver health.

Urinary system (kidneys)

If you have mild kidney disease, you should be able to take Harvoni without any problems. Your doctor will likely prescribe the normal dosage for you. But if you have severe kidney disease, your body may not be able to process the drug well. This could lead to increased amounts of the drug in your body, and increased risk of side effects. Before taking Harvoni, talk with your doctor about whether this drug a good choice for you. And be sure to share all of your medical records with your doctor, including information on your kidney health.

Circulatory system

A more serious side effect of Harvoni is bradycardia (slow heart rate). This side effect usually happens when Harvoni is taken with another drug called amiodarone. Amiodarone is used to treat heart rhythm problems.

Bradycardia typically occurs up to two weeks after you start taking these drugs together. It can cause multiple symptoms because a slow heart rate can prevent your body from getting the oxygen it needs. These symptoms can include:

  • feeling like you’re going to faint, or actually fainting
  • lightheadedness
  • tiredness
  • weakness
  • shortness of breath
  • chest pains
  • confusion or memory problems

If you have symptoms of bradycardia (even if you’re not taking amiodarone with Harvoni), call your doctor right away. This side effect can be life-threatening.

Reproductive system (pregnancy)

If you’re pregnant or planning to become pregnant, talk with your doctor before taking Harvoni. Harvoni is a pregnancy Category B medication. This means there haven’t been enough studies done in pregnant women to confirm whether this drug is safe to use during pregnancy. Harvoni has been tested in pregnant lab animals (rats), but the results of those studies can’t always be applied to humans.

You should take Harvoni only if the potential benefits outweigh the risks to your pregnancy. Talk with your doctor about your health and how this drug could affect your pregnancy. If you decide to have treatment while pregnant, you may be able to enroll in a pregnancy registry. These registries track the results of Harvoni treatment. This data can provide information that can help other women make decisions in the future.