The new law also imposes different limits on how much medicine people can buy.
Missouri previously limited shoppers to two packages per purchase of medicines with pseudoephedrine or ephedrine as the sole active ingredient and three packages per purchase for medicines that contain other active ingredients.
The new law limits people to 9 grams a month of any powder pill medicine containing pseudoephedrine or ephedrine. For gel caps and liquid forms, the 9-gram restriction would apply to each purchase.
Nine grams is equal to 300 tablets of 30 milligram Sudafed, which typically lasts four hours. That means customers could buy about 12 boxes containing 24 pills each month - more than enough to take the maximum dose of the medicine around the clock.