Clinical Trial of High Dose Lisdexamfetamine and Contingency Management in MA Users

The goal of this clinical trial is to learn if administering a high dose stimulant with Contingency Management reduces days of use in adults who use methamphetamine better than the usual treatment provided by the clinic. The main questions the trial aims to answer are: Is a high dose stimulant better than a placebo and usual treatment at helping reduce the number of days they use methamphetamine? Is a high dose stimulant with contingency management better than placebo and usual treatment at helping people reduce the number of days they use methamphetamine? Participants will be placed randomly into one of four groups: 1. Usual treatment and placebo 2. Usual treatment, placebo and contingency management 3. Usual treatment and high dose stimulant 4. Usual treatment, high dose stimulant and contingency management Participation includes the following: 1. Participants will receive medication or placebo weekly for 15 weeks. 2. Participants will attend the clinic for weekly treatment 3. Participants will attend the clinic once every 2 weeks for study visits. Each visit will take about an hour to complete. At these visits, participants will be asked to provide a urine sample and complete questionnaires.