The Texas Attorney General has filed a lawsuit against AstraZeneca that alleges the drug maker illegally marketed its Seroquel antipsychotic pill for unapproved uses, paid kickbacks to physician and state health officials, and subsequently caused the state Medicaid program to overpay for the medicine.

The lawsuit, which was filed this week in a state court in Texas, builds on claims in lawsuits that were filed by two former AstraZeneca sales reps, who alleged the drug maker used various tactics to induce physicians to prescribe...