Can cacti be poisonous

Cacti are not generally considered good to eat. It's a common misconception that cacti have water in them, but you'll find it's more of a slimey liquid that'll probly make you feel ill.

Some cacti, such as Peyote and San Pedro are also psychedelic, as they contain Mescaline. Although not poisonus per se, it would not be advisable to ingest them as food as the experience can last up to 12 hours, which can be terrible under the wrong conditions.

Other than that, there is no danger so long as you don't eat them and stay clear of the spines :)