Inclusion Criteria:

* 18 years or older
* Diagnosed with clinically definite, possible, probably, or lab-supported probable ALS per revised El Escorial criteria
* Breathing assessment called forced vital capacity (FVC) greater than or equal to 50%.
* Able to swallow pills at the start of the study and expected to for the length of the study.
* If on ALS modifying medications must be on a stable dose at least 30 days.
* Experiencing 4 or more cramps per week during a 2-week screening period.

Exclusion Criteria:

* Disease duration \< 5 years
* Tracheostomy invasive ventilation, or noninvasive ventilation of more than 12 hours/day
* Pregnant or lactating, adults unable to consent, and prisoners
* Taking ranolazine or investigational drug or has received an investigational drug within 30 days (or 5 half-lives for drugs, whichever is longer) prior to screening
* Medically uncontrolled comorbidities (heart, liver, kidney disease)
* Baseline QTc interval prolongation \>450 ms for men/ \>470 ms for women, history of long QT syndrome, or medications which prolong the QT interval
* Participation in an experimental drug trial less than 30 days before screening
* Patients have to be on a stable dosage of any medications used to treat muscle cramps for ≥30 days or have been off these medications ≥30 days prior to randomization.

Note: Other protocol defined Inclusion/Exclusion Criteria may apply.

Eligibility last updated 10/17/2024. Questions regarding updates should be directed to the study team contact.