As a baseball guy as well as someone with a deep science background, I thought I'd take a moment to explain some of the stuff we've heard about the Manny Ramirez situation, at least as I understand it.
Firstly, Manny was banned because he tested positive for human chorionic gonadotropin (hCG.) This substance is on baseball's banned list. There are no reports that Manny tested positive for anything else, such as steroids (but see below for more.)
Let's talk about what hCG is. This substance is not normally found in men or women except for one big expcetion: pregnant women naturally produce hCG. This is the molecule for which home pregnancy tests are looking. These tests are extremely accurate, with false positives being a virtual impossibility since hCG is never found in men or women except in the case of pregnancy. (If you want to know how these tests work, I can explain that too, but it's a bit off topic.)
Anyway, because hCG is involved with the reproductive system, it's been found to have certain effects when used as a drug. Most often, it's used as a fertility medication for women trying to become pregnant. Because hCG is a normal naturally-produced part of the process of ovulation followed by fertilization, the ovulation itself can sometimes be stimulated by introduction of an artificial source of hCG.
The drug can also be administered to men, and in this case it can stimulate production of testosterone. hCG is not a substance naturally found in men at all, but because the biochemistries of the reproductive system are not too different between men and women, it's not surprising that hCG has some effect in men.
A couple of things that were reported yesterday were a little confusing, I think.
Firstly, it was reported in some places that hCG and clomid are the same thing. They are not. Clomid is a drug also used for fertility and also when taken by men can stimulate testosterone production. But clomid is purely an artificial substance and not something ever produced by either men or women's bodies.
Secondly, it was reported that hCG is used by steroids users as a masking agent. This is pretty confusing. A masking agent is usually a substance taken that chemically interferes with a test. For example, some steroid masking agents bind up the steroids or steroid products in the urine so that they don't show up on a test. Clomid and hCG don't work this way. What they do is restore a male body's biochemistry back closer to the norm by blocking estrogen production and stimulating testosterone production. An athlete taking steroids would typically take steroids for a certain period of time (usually several weeks) and then take clomid or hCG at the end of the cycle. The thinking is that if the urine is tested after the clomid or hCG has been taken, two things are achievied: steroids and steroid products are are low or non-existant concentrations since the subject hasn't taken them in a while, and estrogen and testosterone levels are within normal ranges for a healthy male.
Yesterday, Scott Boras claimed that Manny was taking hCG under a doctor's prescription and other unidentified people said that Manny was taking the drug for infertility or sexual dysfunction. That last part is bunk--hCG does not treat sexual dysfunction--for example it does not help with erectile dysfunction. It can legitimately be used for infertility in men by stimulating testosterone production that can help with sperm count. However, this is a measure that would be taken only by someone actively trying to conceive a child (which perhaps Manny is...who knows?) If Manny was indeed taking hCG for interfility then he should have access to lots of backup documentation including not only a doctor's prescription but also the fertility tests (such as sperm count or sperm motility tests) that led to the diagnosis. I presume that MLB asked Manny to produce these documents and he couldn't, leading directly to the suspension.
So, in summary, Manny did NOT test positive for steroids but DID test positive for a banned substance, and the particular banned substance, in the absence of any documentation to the contrary, is a very likely indicator that he previously took steroids.