This house rule replaces "Knocking a Creature Out" (D&D player's handbook 198). A concussion is not an anaesthetic.

A creature that is at 0 HP loses all fighting spirit. It surrenders, and is subdued.

• The creature needs to be nearby. The "Knocking a Creature Out" rule assumes mêlée attacks, but here it's OK as long as you can reach it. I.e. not on the other side of a ravine or similar. This is perfect for chases, for example. A chase ends when the quarry gets out of sight, or is subdued.
• You'll need to declare ahead of time that you're fighting to subdue and not to kill.
• This isn't the only way creatures can surrender or give in. It's a replacement for getting knocked out, not a catch-all rule for all surrendering or subduing situations.
• The subdued 0HP creature will accept being led somewhere and/or getting tied up. It's under no obligation to answer questions, speak truthfully, or do actions such as carrying things.
• If you try to force the subdued 0 hp creature to do things like that, it'll start fighting again and fight until death (any hit kills it). Essentially getting extra rounds of combat in.
• Just like a knocked-out creature: a healing word, a healing potion, or a 1d4 hour rest restores the creature's fighting spirit and removes the subdued condition.
• So to interrogate them, or try to convince them to join your side, or similar, hold off until they have at least one HP. Just lock them up or tie them up, that's the limit to the meekness the subdued condition confers. Diegetics ("roleplaying"/"cloud") circumstances, or module text, come into play to see if they'll try to escape their cell / ropes or if they'll give in once they have some HP.
• Or just let them go. They won't hurt you until they've rested. So if you're just passing by…
• XP: Our rule is that an enemy only gives XP once (usually the first time you defeat them). (This is instance identity, not class identity.)