This question comes up fairly frequently, it might be worth having a quick search in the SN children section. A few of us have kids with ADHD, I have ADHD myself. There's a range of opinion, but most people agree that the meds work in most cases - not a miracle cure, by any means, but they reduce the symptoms. The debate is about side-effects and whether the risk of side-effects outweighs the benefits and of course there's no right answer to that one, you have to weigh it up for your kid on your own.
The official NICE guidelines say that therapy and management strategies should be tried first, and that medication should be a last resort. In practice, therapy is incredibly hard to come by and of course it's a moot point how far these strategies will work for a kid with eg ASD. So one of the things to discuss with them next time is what alternatives are actually available in practice and in detail what it would consist of so you can decide if it might help your DS.
My personal view on meds is that in the short to medium term, the side effects seem fairly easy to spot - particularly if your child is high-functioning and can tell you how they feel - and if you have problems you can discontinue medication without withdrawal symptoms. So imo, meds are worth a try. They haven't been in use long enough for us to be sure there are no long-term effects so I'd say review the situation regularly: we realise now that kids don't really "grow out of" ADHD - but the symptoms may change as they approach adulthood and they may learn to manage their symptoms without medication.
As fab says, there are various sorts to try, the usual order is ritalin, strattera, anti-psychotics, just because ritalin is the cheapest and statistically most likely to work. I only know 2 or 3 kids with ASD who have tried ADHD meds and I have to say ritalin didn't work for any of them (and caused sleep issues for one) but that's not really a statistically significant sample.
I personally have been on ritalin for about 18 months - very late diagnosis! Once I'd found the right dose, I had the most common side-effects (insomnia and lack of appetite) for a couple of weeks but then they wore off. I also get a bit of a post-meds slump when they wear off which means I'm a bit below par after about 7pm. Like I say, it isn't a miracle cure by any means, I still have attention issues, but it takes the edge off and makes it more manageable.
Hope some of that helps.