Owing to circumstantial practicalities I will be taking a commercial flight to the USA sometime next month. Accordingly, I will transit at the main border control (I already know what to do when travelling private craft). I will be carrying some prescription medicine which is heavily regulated in the UK and is listed in Schedule IV of the DEA's Drug Scheduling page. But maddeningly, they don't tell you what to do.
There is another drug which is also heavily regulated in the UK and I suspect it is similarly controlled in the USA, but I cannot find it on the above link. It is probably listed under a different name. "Heavily regulated" in this sense means they are explicitly controlled and require a GP's sign off each and every time and you can only get a 30 day supply after which the GP has to sign off again. I am also reliably informed that both drugs have a street value of GBP 20 per capsule. There is also another in the same category, but has a much higher street value (because it is more difficult to obtain, but I do not believe it is an opiate).
I don't need to be specific about their names because the same drugs use different names depending upon whichever provider the Trust is working with at the moment.
I have been trying to find out what the correct course of action is. I am not interested in answers that say I should use deception by silence because I like to play things strictly by the book. If it means I have to fill out some forms or follow the 'red queue' or whatever, that's fine. If it means I cannot bring them that could be a problem because I plan to stay more than a day or so.
I have read (and up voted) 'phoog's' great answer: Taking opiates to the US and my stuff is not necessarily an opiate hence this is not a duplicate question.
Question: what do you need to do if you are transiting the main control point and you have a drug on "Schedule IV" and two more that you don't know where they fit in?
Secondarily: if a given drug is totally forbidden, I assume you have to bring a substitute, please confirm. And will I have to visit the GP and pay the requisite GBP 30 to get a personalised letter?
I will be using my American passport if that makes any difference at all.