When taking any medicine, it's always crucial to follow your physician's exact instructions, but if yours didn't specify, then your second strategy is to follow the packaging information that comes with a prescription medicine.
I can tell you right off that the patient product information states clearly that, "For asthma, SINGULAIR should be taken once a day, in the evening as prescribed, whether or not you have asthma symptoms."
I'm not sure of the rationale behind that recommendation, but I did read a study last year that suggested asthma/allergy medicines may need a few hours to reach maximum effectiveness after you take them, which is why taking them at night can be most beneficial in getting effects the next day.
To your health,
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