This invention relates to pharmaceutically acceptable amphiphilic antioxidant compounds, compositions and dosage forms comprising said compounds, and methods and uses reliant on said compounds. The exemplified compounds are all mitoquinone derivatives, being methoxyphenyl alkyl triphenylphosphonium or methoxy dioxocyclohexadiene alkyl triphenylphosphonium derivatives. The compounds, compositions, dosage forms, uses and methods are useful in, for example, the treatment of diseases or conditions associated with oxidative stress.