Causing sleep or making a person want to sleep -

• Causing sleep or making a person want to sleep -  Soporific
Soporific (noun), (adjective)
English Meaning: Causing sleep or making a person want to sleep.
Bangla Meaning: নিদ্রাকর (পদার্থ, পানীয় ইত্যাদি)। 

প্রশ্নে উল্লেখিত অন্য অপশন গুলোর মধ্যে - 

Sporadic - Not happening or appearing in a pattern; not continuous or regular.
Substantiate - To show something to be true, or to support a claim with facts.
Mitigate - To make something less severe or less unpleasant.

Source: Lecture.