The serum was first seen and administered in Insurgent to Tris Prior after being in a fight with Peter Hayes who tried to steal the hard drive containing the simulation program. However, the Amity that gave Tris the serum didn't take into account her height and weight, resulting in an overdose that placed Tris in a state of euphoria.
The serum's effects can be seen immediately after administration. In small doses, it calms the mind and improves the mood of the person administered. The person may forget why he/she was angry in the first place. A feeling of calmness replaces the irateness of the administered. Dizziness is a common side effect of the serum.
Because the serum's dosage is linked to the person's height and weight, overdosage can be common had the important factors not be taken into consideration. In large doses, exaggerating effects can be evident. A euphoric and overly-elated feeling can be a common effect.
Amity administers it to their faction members who have trouble keeping compliant and peaceful, characteristics that violate Amity's virtues. Johanna Reyes, the Amity's former spokeswoman indirectly confesses after being confronted by Tobias Eaton that they mix the serum on some of the food, particularly their bread.