Research nootropics. There are many, and yes, some improve mental performance. Simply smelling Rosemary oil when learning somethings improves long term memory 40%. There is a lot of research and many products. Some are more effective than others, and some work better for an individual than others. Some people will notice no effects at all and other may see dramatic effects. For most, it is in between those extremes. None will make you a genius if you are not. They may sharpen your performance temporarily. There are some, that with continued use, may encourage neural growth - but, the research is not all that solid. An excellent - if dated - introduction to the topic can be found in the books “Smart Drugs” and “Smart Drugs II”. Some people use “stacks” of different products to achieve a personally tailored effect.
I personally take some supplements, based on my individual needs. I take Vinpocetine (an extract of the periwinkle plant) which has a mild cognitive effect (not really even noticeable) because it also helps to improve eyesight and to protect the brain in case of a stroke (the main reason). I eat a half-dozen eggs every day for choline, and additionally take Huperzine (which reduces acetylcholine reuptake) because with my mental load I can easily deplete my stores of choline and my acetylcholine levels become lower than optimal (I learned that the hard way). The choline doesn’t make me “sharper”, but prevents me from becoming “duller”. I take Gingko Biloba because it increases blood flow to the brain. It may have a very mild effect, but is good for the brain. I use an aromatherapy diffuser with Rosemary when studying.
Those are not everything that I might consider or take ocassionally and there are hundreds of possible products. None are a silver bullet for increasing intelligence. Most of them work by either improving memory or sharpening your focus - usually temporary, although the effects of Rosemary are longer lasting since they affect memory formation rather than memory retrieval.