One cannot bring stuff into the US except for one's own use; if your friend is not staying 6 months and does not take/need the Sumatriptan, you can't get there from here and risk getting your friend in trouble:

Information on U.S. Customs | Embassy of the United States Stockholm, Sweden

OTC drugs are regulated by the FDA too, and have to fill out New Drug Application forms, etc. and prove they are okay to be OTC so I suspect the drug would be "classified" as prescription in this country, no matter where it was bought.