This has been in my collection a long time, and is one I come back to from time to time. The Blue of the title is a drug , instantly addictive, and withdrawal means death.
Who's pushing it, and why?
There are aliens, so it's no great leap to guess they're involved. But there's also opposition to the protag's investigation from the human authorities, so there's no support to be had there.
It's quite dystopian - the writing evokes sleaze and a broken society, and while you hope for a happy ending - there's a race against the clock going on - there's nothing in the author's style that promises you'll get one.
So yes, it's an adventure/thriller, more like the Big Sleep than the Thirty-Nine Steps. The aliens are unimportant in one sense - writing the novel today you could easily substitute terrorists or an unfriendly nation with strong science, and tell much the same tale.