Alka seltzer xs provides fast and effective relief of headaches with an upset stomach it can also be used to relieve migraine period pains toothache sore throats joint swelling and stiffness neuralgia lower back pain sciatica rheumatic and muscular aches and pains muscle tenderness and stiffness sprains strains and symptoms of cold and flu such as feverishness sour stomach also referred to as acid indigestion or upset stomach is a term used to describe abdominal discomfort of