Typical sunflowers that are planted are annuals; however, there is a newer crop being developed called "perennial sunflowers."
it is perennial
perennial
annual
annual
annual plant
annual for eating, biennial for seed saving
Onions are biennials
Sugar cane is a tall perennial grass.
annuals
guava is a perennial plant
Plants can flower regardless of whether they are perennial or annual, so no, blooming does not automatically make a sunflower a perennial.
There are some perennial plants that are toxic, such as foxglove, but there are also many that are not harmful at all.