What to Know About HIV Booster Drugs

Medically Reviewed by Jonathan E. Kaplan, MD on April 12, 2022
5 min read

Your doctors have lots of choices when it comes to which drug combination or regimen you should take for your HIV. They can help you think through your options. Many of the medicines you’ll take help you by fighting the virus itself. HIV booster drugs help, too. But their job isn’t to treat HIV. It’s to make certain other HIV-fighting medicines work better.

Your doctor might call these drugs boosters. Another name for them is enhancers. Doctors have two drugs they can use in this way to help treat HIV. They are cobicistat (Tybost) and ritonavir (Norvir). Ritonavir is sometimes also called RTV.

You’ll likely take either ritonavir or cobicistat along with HIV drugs from a class called protease inhibitors or from a class called integrase inhibitors. Doctors can use several different HIV drugs to treat HIV. All of them help to keep HIV from making more copies of itself.

When ritonavir is given to boost protease inhibitors, it is usually prescribed as part of a combination pill known as Durart (darunavir plus ritonavir) or Kaletra (lopinavir plus ritonavir). Cobicistat is rarely, if ever, given separately and is almost always given in combination with darunavir (Prezcobix, Symtuza) or atazanavir (Evotaz). It can also be given with the integrase inhibitor elvitegravir (Stribild, Genvoya).

Either of the two HIV booster drugs can help inhibitors work better. They both do it by blocking certain enzymes called CYP3A. That’s why you might see HIV boosters called CYP3A inhibitors.

Why block CYP3A? CYP3A enzymes break down antiretroviral drugs that treat your HIV. By blocking CYP3A in your body, the booster slows this process down. As a result, it increases blood levels of the protease inhibitor or integrase inhibitor, and it makes these HIV medicines more effective.

One thing to note is that scientists first developed ritonavir as a protease inhibitor to treat HIV. It does have some activity against HIV at higher doses. But it also tends to come with bad side effects on your stomach at those doses. That’s why doctors don’t typically use it this way anymore.

You often will still find ritonavir listed along with other protease inhibitors. But it’s now used only at lower doses to boost other HIV medicines. Since scientists made cobicistat specifically to block the CYP3A enzyme, it does it more precisely than ritonavir.

You should always take your medicines as prescribed by your doctor. You’ll take your HIV booster with your other HIV medicines, usually in a combination pill. If you forget to take your HIV medicine when you should, take it when you remember unless it’s already about time for the next dose. You shouldn’t take a double dose to make up for one you missed.

Ritonavir usually comes in pill form, usually combined with other HIV medicines. Therefore, you will take it together with your other HIV meds. You should always take ritonavir with food. Cobicistat also comes in pill form, usually combined with your other HIV medicines. You will take it at the same time as your other medicines along with food.

If you are taking your booster medicine in pill form, don’t break or chew the pill before you swallow it. It’s important not to take too little or too much of your booster medicine. If you think you took too much, call your doctor, poison control, or go to the emergency room.

Since you will take your booster medicine along with other medicines, it may be hard to tell which one is causing any side effects. At higher doses, ritonavir can cause side effects such as nausea, diarrhea, headache, and changes in taste. But at lower (booster) doses, these side effects are very uncommon.

Side effects of ritonavir may include:

  • High cholesterol
  • Diabetes or high blood sugar
  • Immune system changes (immune reconstitution inflammatory syndrome or IRIS)
  • Changes in your body fat
  • Kidney stones

It also can cause serious side effects including:

Check the label to see the full list of side effects.

Most people do well while taking cobicistat, as by itself it usually doesn’t cause side effects.

In combination with boosted drugs, it may cause stomach problems. If you take cobicistat with a drug called atazanavir, the most common side effects are yellow skin and eyes (jaundice) and a rash.

Cobicistat may cause kidney problems or may make a kidney problem you already have worse. Check the label to see the full list of possible side effects.

Ask your doctor about anything you should expect or watch for based on the medicines you’re taking. Make sure you know how and when you should call them.

Contact your doctor if you notice any new or troubling symptoms that you think may be related to your HIV medicines. You should call them right away or go to the emergency room if you think you’ve got signs of a serious side effect.

While you’ll always take boosters with your other HIV medicines, you have to be really careful about anything else you’re taking. Because HIV boosters block an enzyme that breaks down medicines, they can have interactions with many other drugs. This means that HIV boosters may affect how other drugs work. Other drugs also may affect how your HIV medicines work.

Tell your doctor if you are taking or thinking about taking:

  • Other prescription medicines
  • Over-the-counter medicines
  • Vitamins or supplements
  • Herbal remedies

Some medicines shouldn’t be taken with HIV boosters. For others, you may need to change the dose. Taking these HIV medicines with certain other medicines may lead to serious and even life-threatening side effects. Your doctor can help you weigh the benefits and risks of any other medicines or supplements you take while treating your HIV.

Your doctor should know other things about you before you take an HIV booster along with your other HIV medicines. Make sure you tell them:

  • If you are allergic to any medicines.
  • If you have problems with your kidneys, liver, or heart.
  • If you have diabetes or a bleeding disorder.
  • If you have any other medical condition.
  • If you’re pregnant or want to get pregnant.
  • If you’re breastfeeding or want to breastfeed.
  • If you’re taking birth control. Hormone-based birth control may not work as well if you’re taking an HIV booster.