Bloodborne has an interesting little glitch that will allow you to duplicate all of your consummable items.
Discovered by Kotaku, the glitch makes item duping very simple. It goes without saying that using the glitch to duplicate your consummable items trivializes the game's challenges so I don't recommend using it unless you're absolutely intent on ruining the Bloodborne experience for yourself.
In order to exploit the glitch, you'll need to create a new character and play until you arrive at Hunter's Dream. Once there, go back to your main character and empty the chest in Hunter's Dream of all its items. Switch back to the alternate character and buy a pebble and store it in the chest–make sure the pebble is the only item within the chest.
Now switch back to your main character and decide what you want to dupe. Put one of the consummable item you wish to dupe in the chest (such as Blood Echoes). Buy as many pebbles as you want to duplicate. Buy a lot of pebbles.
The way the exploit works is that it takes any extra pebbles you can't carry (as there is a carry limit on consummable items) and puts them in your chest. If you're carrying 20 pebbles, any additional pebbles will go into storage. If you buy 10 extra pebbles, you'll get 10 extra duped items in your chest.
Here's a video of the trick:
Expect it to get patched out soon.