According to About.com, how long medicine takes to absorb into the stomach depends on the type of medication, whether it is taken with food or on an empty stomach, and the ability of the medication to pass into the bloodstream. The quickest absorption occurs with medications that dissolve in the mouth and the longest with those having a special coating that enables them to dissolve slowly in the stomach.
Sublingual and buccal medications, or those that are placed under the tongue or in the cheek, are the quickest absorbing medications, as they pass through the lining of the mouth and are effective almost immediately, according to About.com. Most types of capsules and tablets should be taken with water. Using other liquids to take medications, such as milk or grapefruit juice, can inhibit the effects of the medication or cause dangerous side effects.
Additional factors that affect medication absorption rates include the amount of acid in the stomach and whether the medication interacts with other medications being taken, according to About.com. Doctors typically give directions to their patients regarding taking medication on an empty stomach or not, as the contents of the stomach or intestines can interfere with the medication dissolving and passing into the bloodstream. Tablets are intended to be swallowed whole and should not be crushed before taking.