Can you imagine if the penalty for robbing a bank was you couldn't go into a bank for the next two years and you could keep the money you stole? Banks would be hit more than the local 7-11.
The penalty for doing drugs should be that you are financially liable for the money you have earned during that period, including the money from sponsorship and race earnings. Tougher penalties would be nicer but I don't think they will ever happen. The reason people dope is that the benefits are great, money, fame etc. And the only penalties if you do get caught is the loss of your reputation. Sorry if I am stating the obvious.