If you ask for a drug test, be prepared to pay for it. If you think drugs are an issue with the Respondent, the better approach would be to bring witnesses to testify as to behavior and use. Give the judge a reason not to vacate the OP. Consider hiring an attorney to help you respond to the motion to vacate.
I don't believe you will be successful in Christian County to have the court force a drug test in a civil O.P. matter. If you suspect the respondent is on drugs and this poses a risk to you or other protected persons, simply present witness testimony to support your allegations. The judge can read between the lines.
In most circumstances, if you ask for the test then you pay for it. Also as a word of caution, if seen judges order both parties take a drug test even when only one party raises the issue. What's good for the goose is good for the gander I suspect.
Be sure to show up on time for your hearing(s). Articulate each and every reason why you believe the respondent poses a risk to you support by factual examples.
This response is being provided for information purposes only and does not constitute an attorney client relationship. Furthermore, I am only licensed to practice law in the State of Illinois. While there are oftentimes similarities between States' laws, there can also be large differences. You should not rely on this response as legal advice and are highly encouraged to speak to an attorney licensed in your State for an accurate legal answer.