1. Male or female subjects, 16-26 years of age at the time of consent
2. An established diagnosis of ADHD and CUD based on the DSM-5
3. ADHD severity of 4 or greater as determined by the Clinical Global Impression-Severity (CGI-S) scale
4. Subject must be interested in or currently participating in some type of treatment for their CUD, including, but not limited to, outpatient individual therapy, outpatient group therapy, CUD-directed pharmacotherapy, Marijuana Anonymous, Alcoholics Anonymous, or Narcotics Anonymous
5. Subject must report cannabis use on at least 3 of the 7 days prior to study enrollment
6. Subject must have a level of understanding sufficient to communicate intelligently with the investigator and study staff to complete study tasks in English
7. Subject must be willing to cooperate with all tests and examinations required by the protocol
8. Subject must be domiciled in the state of Massachusetts
You may not be if
1. Subjects who are pregnant or nursing, or subjects unable or unwilling to use birth control. Birth control includes, but is not limited to:
* i. hormonal methods, such as birth control pills, patches, injections, vaginal rings, or implants
* ii. barrier methods (such as a condom or diaphragm) used with a spermicide (a foam, cream, or gel that kills sperm)
* iii. intrauterine device (IUD)
* iv. abstinence (no sex)
2. Subjects who present a negative urine dipstick result for cannabis use at baseline or report fewer than 3 use days of cannabis in week preceding study enrollment
3. Subjects with major untreated psychopathology, psychosis, suicidality, or concurrent active non-nicotine SUD other than CUD that, in the investigators' opinion, place them at risk for the adverse effects or need for additional care
4. Subjects who are unwilling or unable to comply with study procedures
5. Subjects who refuse additional substance-related interventions
6. Subjects with known medical risk factors (e.g., known untreated hypertension, arrhythmia, premature family history of sudden death) and active symptoms that, in the investigators' opinion, place them at risk for untoward adverse effects
7. Subjects with previous poor response or poor tolerability to methylphenidate
8. Investigator and his/her immediate family; defined as the investigator's spouse, parent, child, grandparent, or grandchild
9. Subjects who are unable to swallow large capsules
10. Subjects with a known allergy to study medication or known hypersensitivity to methylphenidate HCL or product components
11. Subjects with concurrent treatment with a monoamine oxidase inhibitor (MAOI) or use of an MAOI within the preceding 14 days
12. Subjects who have ever taken Jornay PM in the past
