Do you ever feel like everyone around you is doing some substance to make them work faster or better, and that you'll somehow fall behind or be at a professional disadvantage if yo don't?
My anecdote: In undergraduate engineering, a lot of the people around me were on ritalin. I never felt disadvantaged because I felt it didn't give anyone a clear advantage in the hardest subjects like mathematics or nonlinear control. From what I saw, it didn't seem to improve intelligence that much; rather it helped the distractable people to not get distracted from studying for example.
I felt that sense while I was down in the dumps after going cold turkey ... but now that I have more of a grasp on my life (married, dog, money in savings, living a healthy lifestyle, etc...) I no longer feel that way.
I don't live in Silicon Valley any longer though... so that might be part of the reason I don't feel the pressure.
Right now I might call myself a big fish in a little pond (not really, I am more humble than that) but compared to SF where you are a small fish in a big pond ... there is a lot more pressure to stand-out and be excellent.
