The kind that contains sulfuric acid with high enough concentration to make "carbon monsters" out of cane sugar has got some kick! Put on a chemical apron, face shield, get ready with a pot (no stainless steel!), pour into drain and place pot over drain hole to deflect the rapid ejaculation of boiling hot liquid! That is extremely dangerous. Not sure if banned in the 'States...
Chemical drain cleaners are bad though. If they don't work and a plumber or YOU have to clean it out physically it's another hazard you have to deal with. Most contain caustic (lye) material that will have its way with skin and if splashed in your eyes you will run around and the neighbors will think you are a zombie...
Try a plunger first.
