Adverse effects
Adverse effects occurring in at least 1% of people include:
Central nervous system: headache (7%), dizziness (2%)
Respiratory: upper respiratory tract infection (2%), cough (1%)
Gastrointestinal: abdominal pain (5%), diarrhea (4%), nausea (4%), vomiting (3%), flatulence (3%), acid regurgitation (2%), constipation (2%)
Neuromuscular and skeletal: back pain (1%), weakness (1%)
Dermatologic: rash (2%)Other concerns related to adverse effects are:

Recurrence of Clostridium difficile associated diarrhea
Osteoporosis-related fractures
HypomagnesemiaConcern has been expressed regarding vitamin B12 and iron malabsorption, but effects seem to be insignificant, especially when supplement therapy is provided.Since their introduction, proton-pump inhibitors (PPIs, especially omeprazole) have also been associated with several cases of acute interstitial nephritis, an inflammation of the kidneys that often occurs as an adverse drug reaction. Long-term use
Long-term use of PPIs is strongly associated with the development of benign polyps from fundic glands (which is distinct from fundic gland polyposis); these polyps do not cause cancer and resolve when PPIs are discontinued. No association is seen between PPI use and cancer, but use of PPIs may mask gastric cancers or other serious gastric problems and physicians should be aware of this effect.There is a possible association between long term use and dementia which requires further study to confirm.A review article in U.S. Pharmacist in 2013 states that long-term use of PPIs is associated with decreased calcium absorption (causing increased risk of osteoporosis and fractures), decreased magnesium absorption (causing electrolyte disturbances), and increased risk of certain infections such as C. difficile and community-acquired pneumonia. They hypothesize that this is due to decreased stomach acid production.
Cobicistat, sold under the brand name Tybost, is a medication for use in the treatment of human immunodeficiency virus infection (HIV/AIDS). Its major mechanism of action is through the inhibition of human CYP3A proteins.Like ritonavir (Norvir), cobicistat is of interest for its ability to inhibit liver enzymes that metabolize other medications used to treat HIV, notably elvitegravir, an HIV integrase inhibitor. By combining cobicistat with elvitegravir, higher concentrations of the latter are achieved in the body with lower dosing, theoretically enhancing elvitegravirs viral suppression while diminishing its adverse side-effects. In contrast with ritonavir, the only other booster approved for use as a part of HAART, cobicistat has no anti-HIV activity of its own.Cobicistat is a component of three four-drug, fixed-dose combination HIV treatments. The first, elvitegravir/cobicistat/emtricitabine/tenofovir disoproxil, is marketed as Stribild and was approved by the FDA in August 2012 for use in the United States. The second, elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide, is marketed as Genvoya and was approved by the FDA in November 2015 for use in the United States. Both Stribild and Genvoya are owned by Gilead Sciences. The third, cobicistat, darunavir, emtricitabine, and tenofovir alafenamide, is marketed as Symtuza and was FDA approved July 17, 2018 and is owned by Janssen Pharmaceuticals.Additionally, in existence are a fixed-dose combination of cobicistat and protease inhibitor darunavir (darunavir/cobicistat; marketed as Prezcobix by Janssen Therapeutics), and a fixed-dose combination of cobicistat and protease inhibitor atazanavir (atazanavir/cobicistat; marketed as Evotaz by Bristol-Myers Squibb). Both Prezcobix and Evotaz were approved by the FDA in January 2015.