Other drugs have to be processed by the liver. When you take a pill, the drug goes from the stomach into the intestine, and then to the liver before it is circulated to the rest of the body. A few drugs slow down the kidneys. This increases the blood levels of substances that are normally removed from the body by the kidneys. The most common drug interactions involve the liver.
Several drugs can slow down or speed up the action of liver enzymes.
This can cause large increases or decreases in the blood levels of other drugs that are broken down by the same enzyme. Any pills that you take go through the stomach. Most drugs are absorbed faster if the stomach is empty. For some medications, this is a good thing, but it can also cause more side effects. Some medications need to be taken with food so that they are broken down more slowly or to reduce their side effects.