Reyataz (atazanavir) is a prescription medicine used with other anti-HIV medicines to treat people 6 years of age and older who are infected with the human immunodeficiency virus (HIV). HIV is the virus that causes acquired immune deficiency syndrome (AIDS). Reyataz is a type of anti-HIV medicine called a protease inhibitor. Reyataz comes as a capsule to take by mouth. It is usually taken once a day with a meal or snack. Some common side effects of Reyataz include nausea, headache, stomach pain, vomiting, fever and trouble sleeping.