Inclusion Criteria:

1. Man or woman, 18-65 years of age, inclusive
2. Able to provide informed consent and comply with all study procedures
3. Women of childbearing potential with a negative urine pregnancy test at screening and on adequate contraception
4. Chronic, non-malignant, painful condition, treated with long-acting opioid (methadone, OxyContin®, MS Contin®, Kadian®, Avinza®, Fentanyl®, Opana® ER)
5. Opioid treatment for at least 3 months prior to screening at a minimum dose of 90 mg of morphine equivalents per day or 50 mcg of the fentanyl transdermal patch
6. Dose of opioid treatment stable for at least 1 week prior to screening and expected to be stable from screening through end of second testing
7. Weight at screening 100-300 pounds, inclusive

Exclusion Criteria:

1. Pregnant or breastfeeding
2. Gastrointestinal disorder or S/P gastrointestinal surgery impacting absorption of study medication (delayed gastric emptying, partial or complete gastrectomy)
3. Alcohol or substance abuse within 2 years of screening
4. Consumption of alcohol within 24 hours of a screening or testing visit
5. Consumption of xanthine-containing beverages (coffee, tea, coke) on the morning of a screening or testing visit
6. Impaired kidney or liver function (transaminase levels more than 3 times elevated; estimated creatinine clearance less than 50 mL/min)
7. Epworth sleepiness scale (ESS) score 16 or higher at screening
8. Medically concerning hypertension (≥ 160/100) or unstable cardiovascular illness
9. Any clinically significant illness that would interfere with study participation or put the subject at risk
10. Exposure to investigational medication within 30 days of screening