Our way to measure IQ is build on the core assumption that IQ doesn't really change. Our way to measure depression is on the other hand build on the assumption that depression changes over our lifetime.
We likely need a new way to measure intelligence or stupidity to say well that a treatment increases it within a span of a year.
Yes, IQ tests are medical measurements and they're helpful to medical practitioners. Yes IQ is only loosely related to what we call "intelligence" in the broader sense. The term "IQ" is really consufing because a) it does not measure intelligence and b) it's not a quotient.
It's great to make people more aware of bad mental habits and encourage better ones, as many people have done on LessWrong. The way we deal with weak thinking is, however, like how people dealt with depression before the development of effective anti-depressants:
The only "anti-stupidity drugs" we have are nootropics. But the nootropics we have weren't developed as nootropics. Piracetam was, I think, developed to treat seizures. L-DOPA was developed to treat Parkinson's. No one knows who started using ginkgo biloba or what they used it for; it was used to treat asthma 5000 years ago. Adderall derives from drugs used to keep soldiers awake in World War 2.
And none of them are very good against stupidity. AFAIK, to date, not one drug has been developed by understanding and targeting the causes of different types of stupidity. We have the tools to do this--we could, for instance, sequence a lot of peoples' DNA, give them all IQ tests, and do a genome-wide association study, as a start.
We don't research these things because society doesn't want to research them. People don't conceive of stupidity as a disease that can be cured. We need, somehow, to promote thinking of stupidity as a mental illness. As something drug companies could make billions of dollars off of.