Don’t drugs just get absorbed in the intestine and into the blood stream?

Question: Don't drugs just get absorbed in the intestine and into the blood stream?
- Keywords:
  drug,
  intestine
Asked by 523smbd46 to Natalie on 10 Nov 2015.
- Natalie Garrett answered on 10 Nov 2015:
  
  This is one of the difficulties of designing drugs. A lot of times, you can’t get the drug to cross the intestines (they can get trapped in the mucus and passed out in the faeces, for instance). Also, sometimes they can circulate through the blood a few times but then be excreted by the kidneys in the urine.
  
  The cool thing about the nanoparticles that I work with, is that they are able to cross the gut wall and pass into the blood stream, from there they can travel all over the body and aren’t excreted too quickly. Not only that, but they seem to stick to the coating that is found on blood vessels inside the brain, which gives the drugs inside the nanoparticles more time to dissolve out and get into the brain. We have shown that these nanoparticles are able to increase the amount of drugs that get to the brain by up to 10 times!

Question: Don't drugs just get absorbed in the intestine and into the blood stream?