
As someone who was taht teenager once (albeit not with adhd although i claim living with my sister who did have adhd although in those days it was called 'your mother is a mental whinger go away')....
I got a bloody awful headache and got a rollocking for being stupid....
Not saying this is the greatest advice in the world, but - if you act like this is the hugest deal in the world then it will be (and yes i am fully aware of just HOW dangerous solvents and indeed any drugs can be)...
There is a chance that if you bite back the 'omg swear panic freakout' and give it a bit of 'oh you muppet.... would you like to talk?' you may get further.
Obviously, you know your child and i do not, but i DO know as a f'd up pain in the backside depressed attention seeking teenager, having people go off scale about everything (which of course at 14 in my case, was SO not an issue cos like 'everyones doing it' and 'its no big deal!'), just made me MORE determined and of course made it completely apparent i could demand attention (even if i didnt want it personally but did want to make everyone flap around like headless chickens), and succeed quite easily.
Fortunately one of the very very few things my mother (oh and thats another story indeed) got right was when she discovered i smoked cannabis, was to go 'well its illegal and if you get caught doing that in public or buying it, on your own head be it - id rather you smoked it in the house where its safe if you must' (believe me that wasnt said in a nice way it was said in that hissy scary 'you stupid child i may shortly bury you under the patio' way)....
Because she did that and didnt go OMG MY CHILD DRUGGY, i didnt really see much point - yes i continued to use drugs of various natures but (and im talking cigs, lighter fuel, cannabis, alcohol, not smack or coke or e or speed etc)..... in a much more controlled way, there was nothing to be gained from the 'wind up the parents, see them explode' angle, and i very VERY quickly sussed out there wasnt much to be gained from the supposed 'hey maaaaaan drugs are coooool' angle either.
IF you can make sure as best anyone can that it is made very clear that drugs are not the solution and other methods may prove much better, then my advise is to definately not freak out.
Its nearly 14 years since i as that teenager and im not dead, im not a junkie - ive dealt with my issues and these days i dont drink, i rarely smoke anything dodgy (if i do its because I feel like it having evaluated the situation, in exactly the same way as 99% of the users of this forum decide to have a glass of wine or not, and not because anyone thinks i should or makes me!), my only real vice is cigs (which at 15 i declared id never smoke

)
My sister still struggles with her ADHD (shes now 26) but again shes never had any treatment for it so she would. She is also not a messed up junkie, considering she spent most of her formative years with my anally retentive father who never discusses anything and has the observational skills of a slug, i think thats pretty good going.
I reckon your son will be fine with your support - just dont forget you are NOT alone, this is not some personal hell reserved only for you, others have been there and come out the other end.
Hope my rambling is helpful, if not discard! :)