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Well, klonopin (clonazepam) , belong to benzodiazepine group of drugs , and is used as an anti convulsant ( seizure/fits), an anti anxiety drug ( generalized anxiety , panic attack, OCD , depression) , as a muscle relaxant and as a sedative for insomnia. But , like other benzodiazepines , it is easily and readily abused , and here comes the catch , that is , here comes the problem , as some of the side effects of klonopin are Drowsiness , impairment of thought process and judgment , impaired coordination impaired balance ,dizziness , so , these kind of side effects are enough for someone on klonopin to be termed as unfit for a job requiring attention and presence of mind as well physical endurance .
Well, i do not mean to discourage you by telling these hard facts about the drug you are placed on , but infact , i want you to know them , so that tomorrow , in the interview you go well prepared and present your case very well , as i believe , you should know the side effects of this drug , so that you can refute (discourage) any argument or comment , and tell the interviewer IF at ALL THEY ASK , that you do not suffer from any such symptoms and so are fully fit for the Job.
Also , another thing that is in favour for you is , that you have been legally prescribed this drug , so the question of Abuse does not arise in the first place.
Plus , 1 mg of klonopin/day , is a very normal dose, and more so , it is taken at night , and since , it is usually effective for 8-10 hrs , so by the time it is morning , you have got no substancial effect of it , and you can do your work effeciently without having any side effects of it. But, yes in the test tomorrow, traces of klonopin may be found out, but be confident and honest , place the reason before the interviewers and also tell the positive suportive facts that i have mentioned above , indicating towards no untoward or harmful effect on you.
I wish you Best of Luck , please be confident and do not feel that taking klonopin would be a setback ,as all things are going with you such as legal prescription, no chance of abuse, no side effects , good pysical and mental health , very normal dose of klonopin which is commonly given to so many people , but still they function effeciently , in fact better ..
I hope my answer serves your query according to your satisfaction.