Addictive. They can give you big muscles, but don't give the same results as proper bodybuilding. Your muscles have to grow WITH your body, otherwise they'll be poorly toned. Have a look at some wrestlers, you'll be able to tell the ones who are on steroids by the way their muscles have developed. The ones on steroids will usually have scrunched up veins along their muscles, and will bulge a lot more instead of having a smooth healthy tone to them.
It's harder work, but I would seriously recommend doing things the long way, instead of taking a drug to give you unnatural growth.