The purpose of this study is to determine whether IPX159 is safe and effective in treating symptoms of RLS in subjects with Restless Legs Syndrome.

IPX159 was developed as an extended release formulation to reduce the fluctuation in nefopam concentration compared to IR and to reduce the incidence of peak or rate related side effects.

Inclusion Criteria:

1. Able to understand and willing to sign an informed consent form (ICF) and Health Insurance Portability and Accountability Act (HIPAA) authorization
2. Males and females aged 18-70 with a history of primary RLS for ≥6 months prior to screening
3. Symptoms of RLS by medical history on at least 15 nights during the month prior to Screening
4. BMI 18.5-32
5. Negative alcohol and drug abuse screen
6. Negative serum pregnancy test
7. Agrees to use a medically acceptable method of contraception throughout the study and for 2 months after completing the study.
8. Able and willing to comply with the protocol, including availability for all scheduled clinic visits and telephone calls.

Exclusion Criteria:

1. Subjects who use or intend to use post screening the following medications or medication categories:

   • Sedative hypnotics, trazodone
   • Dopamine agonists, gabapentin, gabapentin enacarbil, pregabalin
   • Narcotic analgesics, other opioids, tramadol, cyclobenzaprine
   • Iron supplementation therapy

2. History of HIV, hepatitis B or C

3. Pregnant or breastfeeding.

4. History of or clinical signs of any form of epilepsy or seizures, excluding fever-related seizures in childhood.

5. History or presence of glaucoma

6. Planning to take herbal medications (eg, hypericum perforatum [St John's Wort], licorice, ephedra, ginkgo, ginseng) during the study.

7. Use of any investigational drug within the last 30 days or within a period of 5 times the drug's half-life, whichever is longer

8. Subjects who, in the opinion of the Investigator, should not participate in the study or are not capable of following the study schedule for any reason

9. Employees or family members of the Investigator, study site, the Sponsor, or Contract Research Organization (if any)