Here's an interesting article which could spark some debate.
Marijuana as a Treatment for Autism?
by Lisa Jo Rudy
I don't think that there's any doubt that "social lubricants" such as drugs and alcohol can make it easier for aspies to temporarily overcome their social problems. It's also true that sometimes these can help them to relax or function better outside of social situations.
Ritalin itself is a stimulant, as is caffeine and nicotine, marijuana (cannabis) isn't clearly defined as either a stimulant or depressant - it has both qualities.
In fact, it's quite common for children to be given ritalin and/or coffee and coke. Less common I think for parents to actually encourage smoking. Marijuana has been shown to have positive effects on depression.
Both Alcohol and Smoking have greater addicition and provide greater physical harm than marijuana but does that actually suggest that it's worthwhile using? In particular, the article refers to a mother who gives marijuana to her 9 year old son for medicinal purposes. It's hard to make a judgement call on something like that.
One thing that it clear however is that these drugs don't act on the autism itself but rather on the symptoms and co-conditions. Ritalin, for example, has no effect on autism or aspergers but does affect adhd. Similarly anti-depressants don't affect the autistic condition, only the symptom of depression.