What effects do the pills that they take have on the citizens in The Giver?

The pill given to those who have reached puberty and over reduce hormonal urges, or "Stirrings" as they are called.

In Chapter Five the morning ritual of telling dreams begins with Lily. Usually Jonas does not have a dream to recount, but this time he relates a dream he has had that has taken place in the House of the Old where he was with Fiona and he wanted her to bathe with him in...

The pill given to those who have reached puberty and over reduce hormonal urges, or "Stirrings" as they are called.

In Chapter Five the morning ritual of telling dreams begins with Lily. Usually Jonas does not have a dream to recount, but this time he relates a dream he has had that has taken place in the House of the Old where he was with Fiona and he wanted her to bathe with him in one of the tubs. Jonas mentions how strong "the wanting" was. He also recalls how pleasurable it was to consider Fiona with the new feelings.
After his sister departs for school, Jonas's mother detains him in order to explain that his "wanting" was an indication that the Stirrings have begun in him. And, it is then that Jonas recalls hearing the Speaker mention that Stirrings must be reported so that treatment could begin.

Before Jonas leaves for school, his mother has him take the appropriate pill that curbs these Stirrings. As he rounds a corner on his bicycle, Jonas's memory of the enjoyment in the Stirrings begins to fade, even as he briefly tries to recall the pleasurable feelings.

In the effort to attain a perfect society, anything that might arouse strong feelings has been eliminated. The people do not see color, they must not use emotional words; they adhere to Sameness in order to avoid conflicts. Individuality is sacrificed to conformity. In the long history of mankind, the strongest feelings in anyone have been those generated by hormones; for this reason, the Community strictly controls these Stirrings in order to maintain peace and contentment. But, it is Stirrings, more than any other quality in people, that truly makes them human, bringing them all the emotions that compose their very souls.