Who has to take the treatment for Stirrings in The Giver?

All adolescents take treatment for Stirrings as soon as they hit puberty.

“Stirrings” is the community’s euphemism for puberty.  Because controlling the size of the population and ensuring a total lack of emotion among citizens is top priority, parents are trained to recognize the earliest signs of puberty in their children so that they can be given pills to stop it.

It is clear that all aspects of daily life in the community are regulated.  It is important that no one ever feel uncomfortable, so the community is designed to prevent people from having the ability to fall in love.  Love may be a wonderful thing, but it also causes pain.  The prevention of pain and instability is paramount in Jonas's community.

Jonas’s parents first recognize that he is having Stirrings when he tells them about a dream he has about his friend Fiona.  In the dream, he is trying to get Fiona to take a bath. It is his first sign of sexual maturity.

"Jonas," she said with a smile, "the feeling you described as the wanting? It was your first Stirrings. Father and I have been expecting it to happen to you. It happens to everyone. (Ch. 5)

At this point, Jonas begins to take pills to prevent the Stirrings from returning.  Since stopping the pills will result in a return of the feelings, Jonas and all other adults are supposed to take them until they are too old to produce offspring.

The side effect of the pills is that they numb people.  The pills do not just prevent sexual attention in adolescents and adults, they also limit access to human emotions.  They basically keep the populace childlike.  A community of children is much easier to control.

After Jonas has received enough memories to understand the world at a deeper level, he stops taking the pills.

He had not taken the pills, now, for four weeks. The Stirrings had returned, and he felt a little guilty and embarrassed about the pleasurable dreams that came to him as he slept. But he knew he couldn't go back to the world of no feelings that he had lived in so long. (Ch. 17)

Not taking the pills is another thing that makes Jonas unique.  He has come to understand that no one in his community has ever had a real emotion.  They do not really understand life and can’t relate to him.  He has problems relating to them too.  He asks his parents if they love him, and tries to convince Asher not to play war games.  Each incident results in him feeling more and more distant from the others in his community.