Inclusion Criteria:
1. Between 18 and 55 years of age at enrollment in the parent ASCME trial;
2. Diagnosed with a moderate to severe MUD as defined by the DSM-5 criteria;
3. Enrolled in the parent ASCME trial and completed the study up to and including the end of study visit at Week 20, Day 1;
4. Interested in avoiding relapse, decreasing methamphetamine use, or abstaining from methamphetamine use;
5. Presence of ongoing substance use, craving, or significant risk of relapse that according to the study physician, warrants extended treatment for MUD;
6. If female:
- Be of non-childbearing potential, defined as (i) postmenopausal (12 months of spontaneous amenorrhea and ≥ 45 years of age); or (ii) documented surgically sterilized (i.e., tubal ligation, hysterectomy, or bilateral oophorectomy); or
- Be of childbearing potential, have a negative pregnancy test at screening, and agree to use an acceptable method of birth control throughout the study;
7. Willing to be randomized to one of 2 study arms and followed for the duration of the trial;
8. Able to start the study intervention within 28 days after completing the ASCME main trial (study no. CRISM-002);
9. Able to provide informed consent;
10. Willing to comply with study procedures;
11. Able to communicate in English or French
Exclusion Criteria:
1. Symptomatic or advanced cardiovascular disease (e.g., advanced arteriosclerosis), moderate hypertension; confirmed current hyperthyroidism; known hypersensitivity or idiosyncrasy to the sympathomimetic amines or glaucoma or any disabling, severe, or unstable medical condition (including electrolyte disturbances) that, in the opinion of the study physician, precludes safe participation or the ability to provide fully informed consent;
2. Any severe or unstable co-morbid substance use disorder that, in the opinion of the study physician, precludes safe participation in the study;
3. Participants with Opioid Use Disorder (OUD) who have been on Opioid Agonist Treatment (OAT) for <12 weeks, and not yet at stabilization dose, or at stabilization dose <4 weeks;
4. Current or a history of any serious psychiatric disorder (e.g., bipolar disorder, pre-existing psychosis, schizophrenia) that, in the opinion of the study physician, precludes safe participation in the study;
5. History of a SAE, hypersensitivity or known allergic reaction to LDX-01 or other amphetamine drugs, or hypersensitivity to the sympathomimetic amines;
6. Pregnant, nursing, or planning to become pregnant during the study period;
7. Planned extended absence during the study period (e.g., pending legal action, surgery, incarceration, inpatient residential program) in the opinion of the study physician that might prevent completion of the study;
8. Use of an investigational drug for stimulant use disorder during the 30 days before screening, confirmed via self-report or pharmacy records; excluding the use of study medication in the parent ASCME trial;
9. Use of prescribed amphetamine-type medication or medication for the treatment of stimulant use disorder (e.g., methylphenidate, modafinil, bupropion, or mirtazapine) in the 4 weeks before screening;
10. Current or anticipated need for treatment with any medication that may interact with LDX-01 (e.g., monoamine oxidase inhibitors \[MAOIs\]) used currently or within the past 14 days and that would preclude study participant at the discretion of the study physician;
11. ECG measurement (Bazett method for the correction of QT interval) that indicates a prolonged QTc interval (≥460 milliseconds for females and ≥450 milliseconds for males) at screening;
12. Any SAEs related to the study product in the parent trial phase that, in the opinion of the study physician, precludes safe participation in the extension study;
13. Any compliance issues related to the study product and/or study procedures during the parent trial phase that, in the opinion of the study physician, precludes safe participation in the extension study.