New pharmaceutical compositions extracted from Ferula assa-foetida are confirmed to effectively treat influenza A (H1N1) virus. The extraction method of the new pharmaceutical compositions mainly includes steps of: (a) extracting F. assa-foetida with methanol to obtain a crude extract; (b) fractioning the crude extract with n-hexane-methanol to obtain a methanol extract; (c) fractioning the methanol extract with chloroform-water to obtain a chloroform extract; and (d) chromatographing the chloroform extract to obtain the pharmaceutical compositions, which can be further fractioned and chromatographed to obtain various sesquiterpene coumarins.