Okay, basically, the more mass you have, the more drug that's needed to exert the same effect on you. But is it really linearly proportional like that? I mean, if you increase your body mass, you're not going to increase the amount of blood in your major arteries and veins. The amount of blood in them is fairly fixed (or is it?) Rather, you'll increase the amount of blood in more peripheral blood vessels. How much does this amount of blood scale with increased mass? Is fat tissue more vascularized (on average) than other types of tissue? Or not? Furthermore, is it a valid assumption that a drug will diffuse "equally" throughout the body, including all of the body's capillaries?