Unfortunately, we do not own the copyright on the NIDA image. We used to have a full size printed poster version, but don't currently know where it is. The small image we have on the site you asked about is the only easily available one we have. Perhaps some more web searching might reveal something larger.
Overall, US government-produced documents have weak copyrights and they tend not to enforce the ones they have, so you probably won't run much risk by using it.
If, for instance, it was done by some famous artist who was not on the payroll of NIDA when he did it, but it was commissioned, that artist or their family could sue you for use of their owned work, but that seems really unlikely.
Anyway, we can't grant you permission since we don't own it, but the risk of using it seems very small to me,