Am I correct to assume that drugs taken orally work by being absorbed by the intestines?

Hey I might have a parasite & was wondering if their presence can weaken drug absorption? After all, parasites can weaken the intestines' ability to absorb nutrients so why wouldn't the same go for drugs, assuming the drug was taken orally? Does it matter what type of drug it is & what type of parasite it is? Would a parasite affecting the intestines be sure to cause troubles for drug absorption? Would it just slow down the drug absorption or would it actually make a lot of the drug useless, perhaps even stealing it for itself?

Other then parasites, are there any other conditions that can weaken drug (taken orally) absorption? Which are these, if any? & would it matter what kind of drug?