The genetic makeup of an organism is what dictates the creation of the different parts of their body and function. Any deviation from what your genome ment you to be is due to environmental factors, accidents, your/your mother's [when she was pregnant with you] actions, etc.
It affects the speed of delivery of drugs throughout the body.
When a person intakes drugs, the drug is disintegrated in the stomach and are being distributed to different parts of the body later on. The more adipose tissues (fat) a body contains, the harder the job will be for the vessels to deliver chemicals to different parts of the entire body.