Psychedelics certainly do have the potential to positively affect mental processes, but I am not sure if IQ is one of those. IQ is a strange thing. It is measuring something, but we don't know just what. "Smarter" people tend to have high IQ's but intelligence is something that can't be measured on a single numerical scale. We really don't have a good definition of intelligence or what abilities constitute intelligence. There are different types of intelligence that depend on different neurological functions.
I like to think about intelligence in terms of a brain-computer analogy. Intelligence(IQ perhaps) measures the power of the hardware, giving a maximum potential of what is possible. Intellect, personality, creativity, motivation, discipline, etc. are analagous to the software, or what can be done with the hardware.
Outside of treating mental illnesses, I don't think any available drugs, psychedelic or otherwise, are going to do much for the former. Genes and early life health are the main factors in what hardware you get. However, there is no doubt that the latter can be affected by drugs.
So no, lsd isn't going to help you do your calculus homework any faster, but it can help you in less linear disciplines.