If you buy used bricks, then you might be concerned about where they were used and if it was in an industrial process that deposited some heavy metals onto their surface. Assuming new brick, it is probably less toxic than treated wood. I think it would be a good idea to get a soil lab to test for heavy metals in your soil a few months after you build a new raised bed for growing food, just to be sure. Heavy metals are more common than people understand. In the Bay Area, a lot of the soil is contaminated with nickel, and guess what: my own heavy metals test shows very high levels of nickel in my blood and hair.

Bricks are made from clay and some lime or in some cases clam shells. Cinder blocks are made from ashes with a lot of clinkers. The ashes are usually coal ash and wood ash doesn't have near the clinkers as coal ash. Since you shouldn't use coal ash in a garden, nothing but wood ash I wouldn't use cinder blocks. That said, most new blocks these days are made from concrete so those should be safe.

It might depend a little bit on the brick, like if it's reclaimed from a nasty site. Or if it's reclaimed brick and it isn't stable and ends up breaking down too much.

Most brick is often "safer" than a lot of treated wood IMO. But are you talking about bricks, or cinderblocks? And if bricks, what kind? In the midwest, big red clay, rough and holed red, and cream city are all common. Where you are or what you have might be different.

A used supply of cinderblocks? I wouldn't worry about it. If there was new leeching to be done, it's probably done.

Thanks everyone for responding. They are bricks and not cinder blocks. The bricks are recycled from a friend's patio/walkway and are in very good physical condition - no cracks, chips, clean, etc. Your comments are very helpful.

Nice bricks reclaimed from a patio? I think you should be fine.