A number of years ago I had the opportunity to speak with a Finnish journalist; we got to talking about track and field; one of the areas he covered as part of his journalistic duties was sports.
The Finnish steeplechaser referred to above somewhere was probably Pekka Paivarinta; he came out of nowhere and broke the world record. It turns out, according to my journalist friend, Paivarinta's brother was a doctor. That's perhaps where blood doping got its start.
He further told me that, with the exception of Viren, he knew for a fact that all the notable Finnish runners at that time were using drugs; I forget now whether he said steroids or blood doping, or both. As for Viren, he said he didn't know, but only strongly suspected.
He said he himself took steroids to see what the effects might be. The main benefit was improved recovery. Without steroids you could work out hard once every other day. With steroids you could work out three times a day and "feel like a bear."
He recalled that in Munich he was situated right next to the track, along with the other official journalists, and in one of the heats of the 5000 Juha Vaatainen ran up alongside Ian Stewart, laughed at him, and pulled away on the straight to win the heat. I looked it up later; heat 4. Vaatainen failed to medal in the final, after having won both the 5000 and 10000 in the European championships the year before. The explanation? Blood doping has a two-phased effect: a positive effect first, followed by a negative effect. In Munich the Palestinian attack delayed the 5000 final, and that put Vaatainen into the negative phase, and he wasn't a factor.
I can't help thinking that nowadays everybody uses drugs, at least those who line-up for the final. It's probably been going on for quite some time, at least since 1960 -- not everybody then, but probably Germany and a few others. The Wehrmacht used speed in WWII, after all.