Linked from
The 7 pages that link to Papaver somniferum, each with the reason it gives.
MorphineRelated: Its latex is the natural source from which morphine is obtained.
OpiumBroader topic: Its seed capsules are cut to collect the latex that dries into opium.
PapaverineRelated: Papaverine occurs among the alkaloids of the opium poppy.
ThebaineNarrower topic: The plant produces thebaine in its latex alongside other alkaloids.