Nearly 9 of every 10 pregnancies among opioid-dependent women is unplanned. Unintended pregnancy results in many costly adverse consequences for both mother and child; treatment of neonatal abstinence syndrome (NAS) alone costs more than $700 million annually. Despite these dismal figures, we know of no efficacious interventions for decreasing unintended pregnancy among opioid or other illicit drug users. We developed and are pilot-testing an intervention to increase prescription contraceptive use by opioid- maintained (OM) women that is delivered in their OM treatment clinic. Usual care in many OM treatment clinics involves giving out information about contraceptive methods and referring patients to family planning providers in the community. The proposed intervention adds (1) the World Health Organization's (WHO) contraception protocol and (2) financial incentives for attendance at protocol visits. At the first intervention visit, OM women receive assistance with choosing a prescription contraceptive method, are provided structured educational counseling about and a free supply of their preferred method, and are offered the option of initiating it immediately. At subsequent intervention visits, they receive support to manage side effects and problem-solve compliance problems, free refills of their chosen contraceptive method, and assistance with switching methods when indicated. They also earn financial incentives contingent on their attendance at each of these regularly scheduled visits. Our ongoing Stage IB pilot trial data strongly support the feasibility and initial efficacy of this intervention, with 5-times more OM women assigned to the experimental intervention using prescription contraceptives at the end of the 6-month intervention compared to control condition women. Building on these promising pilot data, the present application proposes a fully randomized controlled Stage II trial to rigorously evaluate the efficacy and cost-effectiveness of this innovative intervention. OM women at risk for unintended pregnancy (N=195) will be randomly assigned to one of three study conditions: (1) usual care; (2) usual care + WHO contraception protocol; or (3) usual care WHO contraception protocol + financial incentives for attendance. Contraceptive use by all participants will be evaluated at follow-up assessments scheduled 1, 3, 6, and 12 months after trial intake. This design will allow us to more fully assess the efficacy of the intervention while also allowing us to isolate the contribution of the WHO and financial incentives components, both key objectives of Stage II intervention development. Cost-effectiveness will be evaluated by assessing the incremental costs of each additional opioid-exposed pregnancy prevented and birth avoided. The proposed research has the potential to establish the first efficacious and cost-effective intervention for increasing prescription contraceptive use in illicit drug users. The research may also produce important new insights into contraceptive decision-making that will aid in the development of more efficacious interventions for other populations of women at risk for unintended pregnancy.