S-alkylsiothiouronium derivatives such as S-ethylisothiouronium diethylphosphate are used for the treatment of headaches, in particular, migraines, as well as for the prevention or treatment of nausea and vomiting. The compositions of the invention are also effective in preventing or alleviating emesis associated with migraines or other medical conditions such as chemotherapy or radiotherapy, as well as other symptoms of migraines including phonophobia and photophobia.