Doom Patrol & Drug Prohibition
If you ever look at a drug statute (like this one), you'll see a long list of chemicals. The state cannot merely say "All non-FDA approved drugs are illegal;" they have to name the drugs that carry criminal sanctions. This is because the public must be put on notice as to which drugs and chemicals are illegal. If the state doesn't specifically say "This chemical/drug is illegal," then there's no way for an individual to know whether he's breaking the law or not.
The makers of designer drugs used to exploit this characteristic of the law by manipulating existing drugs to create new ones that weren't yet illegal. But in 1986, the Controlled Substances Act made all possible variations of existing drugs illegal, thus heading off such extralegal innovation. Also, if a new drug is sold on the premise of being similar in effect to an existing illegal drug, criminal charges can result.
However, if one had to guess from the side effects as presented in the issue (it makes the user somewhat psychic), Nudge's drug doesn't look to be a variation of any existing illegal drug. It looks to be something totally new, and the doctor's comments back this up. If that's the case, then Nudge's drug is not yet illegal and she can't be convicted of a crime for possessing it. If it's merely a variant of a fictional DCU illegal drug, then it could still be illegal.
However, even though Nudge probably isn't guilty of a crime, I'd argue that it was still OK for her to be arrested under the circumstances. She was found in possession of what was clearly a drug, which had killed other kids who had used it. Cops aren't chemists, and can't make the determination of whether this particular mysterious drug is an illegal variant or a brand-new, from-scratch creation. That's a determination for the crime lab to make. The arresting officer only needs probable cause of a crime, and I think the situation provides for that much.