Dream sharing is the practice of creating a dream and bringing one or more people into that new dream world. While dream sharing, the dreamer creates and controls the world, while the subject populates it with both people and information.
To initiate dream sharing, special medication is needed and is facilitated by the PASIV device. Somnacin is one of the drugs used for this purpose. When dreaming on only one level, a timer mechanism on the PASIV device can be used to wake up dreamers. Multiple dream levels require a method known as a kick to awaken from a dream on a deeper level.
Dream sharing was first utilized by the military to provide a realistic training method for soldiers, in Project Somnacin. Underground circles have also utilized dream share for entertainment purposes, such as "dreamcades" for challenging others and creating dreams for leisure. In Inception, dream share is used to commit extractions by stealing information and inception by planting information in the form of an idea into the mind of the subject and making the subject think that the idea is their own. Miles brought Dominick Cobb and the others into dream sharing to prove to them that their creativity was limitless.
Overexposure to dream sharing can cause an individual to be unable to dream naturally. Many people who can no longer dream must use a PASIV device if they wish to dream while they sleep.
Yusuf: "Binds the dreamers tight. Let's them dream as one. Makes it real. Of course, if you'd prefer, you could use Somnacin brand. If you could explain to the international control council what you wanted it for."
Arthur: "That's why the military developed dream sharing - a training program where soldiers could strangle, stab and shoot each other, then wake up."
- Inception: The Big Under
Saito: "Why do they do it?"
Yusuf: "Tell him, Mr. Cobb."
Cobb: "After a while... It becomes the only way you can dream."