>>11709433Most drugs are chemically similar to substances already in our bodies. That way our immune system doesn't immediately recognize the drug is there and it can slip past a lot of the bodies defense mechanisms and get to where it needs to go. Also it is more likely to fit into some receptor where the drugs effects are manifested. Of course this is a huge oversimplification, but it means random chemicals we find in space are very unlikely to be biologically significant, beyond just being poisonous. Or if it's a chemical that's a part of alien biology it's unlikely to be active within our biology.
