To build a raised garden bed you'll need timber suitable for in-ground use, which is typically H4 treated pine.
If you are looking for an alternative to traditional CCA treated timber, the Micropro Sienna sleeper range would be a suitable option. There are limited options when it comes to posts with a non-CCA treatment. I would suggest you either use the Whites Retain-iT system or sleepers for the posts as well.
Microshades are awesome. No need for any lining just screw them together and away you go, hardwood is fine also. Hardwood posts are easy as, and or use galvanised brackets to keep them together. - TheSaltyreefer
Microshades sleepers are excellent and considered 'safe'. That's what I use in all of our food garden beds here at home. Hardwood, if you can find it untreated, is also excellent but harder to cut, lift, etc. Be aware that a lot of hardwood is CCA treated so look carefully at product details. Some people will suggest recycled railway sleepers. I would advise against that. Apart from being crazy-hard to work with they can be heavily impregnated with all manner of industrial grade chemicals. - Adam_W
The difference between the CCA-treated timber and the Microshades sleeper is that it does not contain any Arsenic. This one single difference makes the Microshades sleeper an ideal timber for use in garden beds. The treatment on the timber is done by pressure. No other treatment is made prior to this.