Sonja believes that the pill prescribed to her by the doctor has cured her of anxiety disorder. However, the pill contains no active ingredients. Sonja's belief that she is better now is an example of the effect.

Placebo

Explanation:

Placebo effect is the concept that illustrates about people experiencing some kind of advantage or benefit through association or taking inactive substance or treatment in their lives.Placebo is the factor that actually has no effect.

According to the question,Sojna is under placebo effect in which she is thinking about betterment occurrence in her anxiety disorder due to pill consumption but in reality there is no active ingredient in pill to treat disorder.  

i need !

good question. i'll be looking into that. (this is a joke sir)