Gardasil is a prescription medication that is used in the prevention of cervical cancer, genital warts, and various precancerous genital lesions that are caused by certain types of human papillomavirus (HPV). Gardasil has been approved for use in girls and women age 9 to 26, and works by stimulating the immune system to produce antibodies to fight off the HPV virus. There is only one dosage for Gardasil, regardless of weight or age, and it is given in a three-shot series over a six-month period. As with any medication, there are potential side effects of Gardasil, including nausea, dizziness, and reactions at the injection site.