Ritonavir is used to boost the effects of protease inhibitors. It may be marketed under the name Norvir, but generic versions are available.

You should not take ritonavir with any of the following drugs: alfuzosin, amiodarone, astemizole, bepridil, avanafil, chlorazepate,  cisapride, colchicine, diazepam, dihydroergotamine, dronedarone, elbasvir/grazoprevir, ergonovine, ergotamine, estazolam, flecanaide, flurazepam, fusidic acid, lovastatin, lurasidone, ombitasvir/paritaprevir/ritonavir, methylergonovine, midazolam taken orally, pethidine, pimozide, piroxicam, propafenone, quetiapine, ranolazine, sildenafil (for hypertension), simvastatin, St John's wort, terfenadine, triazolam, vardenafil.

Ritonavir interacts with many other medications and can change blood levels of one or both drugs. Consult your doctor or HIV pharmacist before taking any other drugs with ritonavir or a ritonavir-boosted drug. This includes: calcium channel blockers, drugs for heart conditions, anticoagulants, asthma and allergy drugs, proton pump inhibitors and H2 receptors, indigestion remedies, anti-fungal treatments, anticonvulsants, anti-TB drugs rifabutin and rifapentine, immunosuppressants, some chemotherapy drugs, steroid-containing inhalers, nasal sprays, eye drops, creams, as well as medicines bought from a high-street chemist, herbal preparations and recreational drugs.

Methadone levels may be reduced by protease inhibitors, and require an increase in dose to achieve the same effect.

Protease inhibitors may reduce the effectiveness of some hormonal contraceptives (such as the pill, patches or an implant). If you are using this type of contraceptive to prevent pregnancy you may need to use an additional or different type of contraception.

Changes in heart rhythm, severe allergic (hypersensitivity) reaction and rash (Stevens-Johnson syndrome).

Common (at low dose): Raised lipid levels, diarrhoea.

Take with food to reduce nausea. Do not chew, break or crush tablets. Ritonavir tablets and the powder for oral suspension should always be stored at room temperature.

The usual adult dose is 100mg or 200mg taken once or twice a day, depending on the frequency with which you take the protease inhibtor it is boosting). Ritonavir is available as a generic drug so its appearance will vary. Ritonavir is also available in the combination tablet Kaletra.