Trust me on this.
1 Keep that email.
2 Print it out and mail it to yourself.
3 Email it to yourself.
4 Send him a reply that states you do NOT do drugs. You don't have to be serious. Just say something like "man, it really makes me cringe on the inside when you say stuff like that"
5 Do not visit EF or any other roid related websites on your work PC. Clear the history in your cache.
6 Keep a copy of the reply you sent him on your PC, email it to your home account and print it off.
Now on down the road when the economy is still bad, you are pissed off at this guy or you just need some bargaining power, etc.. you have this copy. Number 4 above is critical. It gives a reply that is negative and it will (A) only encourage him to make more cracks (B) show that your statement is that you do NOT do drugs. Also, make a remark in passing to a supervisor. Something light hearted. Like, "I had a flat tire this morning. That is why I am late, if I used as much steroids as So-So says I did, I would have just picked my car up and jogged here."
Trust me, lawsuits are the thing of today.