Effect of Terazosin on ATP Levels in People With Amyotrophic Lateral Sclerosis

This will be a single center, randomized, double-blind, placebo-controlled pilot study to assess the safety and tolerability of terazosin (TZ) at a dose of 5 milligrams (mg) per os (PO) daily for patients with amyotrophic lateral sclerosis (ALS). The primary outcome of this study is to determine whether TZ increases adenosine triphosphate (ATP) levels in ALS. The investigators will measure adverse outcomes, safety, and tolerability of taking TZ. Procedures include blood draws, spirometry, fluorodeoxyglucose-positron emission tomography (FDG-PET) scans, questionnaires, and physical examinations. TZ will be titrated up to 5 mg PO daily. This is a pilot study and is not powered to assess efficacy of this medication. The investigators' hope is that this study will guide future studies of this (and similar) medications for the disease modification of ALS. This study also aims to learn more about how patients produce and use energy and if TZ can help to reverse energy deficits that appear in ALS.

INCLUSION CRITERIA * Ages 18 - 80 years old * Diagnosed with ALS based on Gold Coast Criteria * ALS symptom onset within 36 months at enrollment * Slow vital capacity (SVC) greater than or equal to 65% * Riluzole use-Never taken or taking a stable dose for at least 4 weeks prior to screening visit or will refrain from starting for the duration of the study * Edaravone use-Never taken or completed at least one cycle (typically 14 days) prior to screening visit or will refrain from starting for the duration of the study * Must have the ability to swallow pills at the time of the screening visit, and in the principle investigator's opinion, have the ability to swallow pills for the duration of the study * Willing to use highly effective contraception for the duration of the trial treatment and for a duration of 80 days after the last dose. EXCLUSION CRITERIA * Orthostatic hypotension at screening is defined as decrease in BP \> 20 mmHg systolic or \> 10 mmHg diastolic and HR increase \