This is a single-center, phase 2 randomized clinical trial of tamoxifen on mean percent predicted isometric muscle strength in patients with amyotrophic lateral sclerosis (ALS). The purpose is to determine whether the triphenylethylenetamoxifen, used as adjuvant therapy in the treatment of breast cancer, can delay the loss of isometric muscle strength in ALS patients.

Inclusion Criteria:

• clinically probable-laboratory supported, clinically probable, or clinically definite amyotrophic lateral sclerosis

Exclusion Criteria:

• Allergic or idiosyncratic response to tamoxifen.
• Other active neurologic diseases that may produce weakness, sensory loss, or autonomic symptoms.
• Psychiatric, psychological, or behavioral symptoms that would interfere with the subject's ability to participate in the trial.
• Clinically significant cardiac, pulmonary, gastrointestinal, hematologic, or endocrine (poorly controlled insulin-dependent diabetes mellitus or hyperthyroidism) disease that may confound interpretation of the study results.
• Previous kidney or pancreas transplants.
• Significant hepatic or renal disease (AST > 5 times normal, serum creatinine > 2.0 mg/dL for males or > 1.8 mg/dL for females).