Some of your perceived cognitive improvements while on the drug are probably just that: perceived, not actually objective. Self-observation won't work too well here I don't think.
Originally Posted by Blarraun
The best test is doing things like maths or programming, or playing chess, thinking, reading with comprehension. See how long it takes you to reach similar efficiency today and monitor it over the next few months. You won't notice slight changes, but if there's anything significant you should be able to tell.
I'm not sure how well that would work. Math and programming, maybe. In both of those cases you could easily interpret the increased focus derived from the methylphenidate as increased intelligence. Chess is a lot more practice-based than it is intellect-based, which is why it's annoying when people put chess grandmasters on the top of lists for "smartest person in the world" or something like that. It's also not very equable; your opponent changes, as do the circumstances of the game, leading to a decent possibility for error.
You could try an IQ test, but I don't think that would work very well. You'd get better with each retake, and changing the test you used each time wouldn't be standardized. This
one's decent if you do decide to try that.
One very subjective way of measuring a specific type of intelligence is via writing. Write a short fiction piece (or even just a fraction of a longer fiction piece) while on the drug, then while sober. Make it about 2000 words or so. Do it a couple of times for both states. Make sure you indicate which state you were in while you wrote it, and don't plan out what you're going to write in advance (so you can also measure spontaneous creativity, to a degree). After you've got a decent number of samples, you can judge them yourself and decide if you wrote better on or off the drug. You could also have someone else help. It might be a good idea to wait a couple of weeks before deciding to judge (or even reread) the writing, so that way it's less familiar to you.
also congrats on being the 1600th thread posted in this sub-forum