I wonder if there is anything else before DO and MMO? Because it seems like if a man wants to become MMO he first learns DO, is there something that should be learned before trying DO? And does Pre e problems interfere with DO? (I've read somewhere that it's easier for pre e to learn MMO but just making sure.)

Also, is DO completely safe? Because when I googled it I found a lot of medical sites talking about it like it's a problem and saying how to fix this.