The goal of this clinical trial is to learn if the drug pridopidine works to treat amyotrophic lateral sclerosis in adults. It will also help to learn about the safety of pridopidine. The main question it aims to answer is:

Does pridopidine slow disease progression of ALS?

Researchers will compare pridopidine to a placebo (a look-alike substance that contains no drug) to see if pridopidine works to treat ALS.

Participants will:

Take pridopidine or a placebo by mouth every day for 48 weeks. Afterwards, all participants will take pridopidine for another 48 weeks.

Visit the clinic once every 1-3 months for checkups and tests

This is a Phase 3, randomized study consisting of a double-blind placebo-controlled (DBPC) period followed by an open-label extension (OLE) to evaluate the efficacy and safety of pridopidine administered orally at a dose of 45 mg twice a day in adult participants with early and rapidly progressing ALS. Standard of care treatments (e.g. riluzole, edaravone and Nuedexta) will be allowed as long as participants are on a stable dose for at least 4 weeks prior to dosing. In the DBPC period, participants will be randomized in a 3:2 ratio to the pridopidine and placebo arms.

In the DBPC period, participants will receive pridopidine or placebo for 48 weeks. In the OLE period, all participants will receive pridopidine for 48 weeks, while maintaining the blind to their original randomization for both the participant as well as the Investigator and other clinical staff. The total study duration per participant will be 102 weeks including screening and follow up.

Throughout the study, participants will be assessed through on-site clinic visits and virtual visits (via telephone).

Key Inclusion Criteria:

• Definite ALS or Probable ALS using the El Escorial criteria.
• Symptom onset of ≤18 months at screening.
• Slow vital capacity (SVC) greater or equal to 60% predicted.
• Treatment Research Initiative to Cure ALS (TRICALS) Risk Profile Calculator score, based on the European Network for the Cure of ALS (ENCALS) survival prediction model, in the range of -6 to -2, inclusive, at screening.
• Able to swallow a capsule.

Key Exclusion Criteria:

• Presence of tracheostomy or permanent assisted ventilation.
• Clinically significant heart disease, clinically significant history of arrhythmia, symptomatic or uncontrolled atrial fibrillation despite treatment, or asymptomatic sustained ventricular tachycardia, or presence of left bundle branch block.
• Presence of unstable psychiatric disease, cognitive impairment, dementia or substance abuse that would impair ability of the participant to provide informed consent and participate in the study.
• Clinically significant and/or unstable medical condition (other than ALS) that may either pose a clinically meaningful risk to the participant and/or to study completion.
• Use of medications that prolong QT interval.
• Previous treatment with pridopidine, gene therapy, or antisense oligonucleotides.
• Confirmed mutation in the SOD1, FUS or C9orf72 gene.
• Pregnancy.