Adults and teenagers aged 17 and above are advised to use one 17-gram packet of Miralax a day as needed, as stated by Drugs.com. The powder should be mixed with a 4- or 8-ounce glass of tea, coffee, water or juice. For children below the age of 16, a doctor should be consulted for the correct dosage..
The powder should completely dissolve in the liquid before being taken. This medication should not be used for more than two weeks, according to WebMD. The use of Miralax is expected to work within seven days. A person should consult a doctor if there is no improvement. Miralax is used to treat constipation.