Original post by MosterGuruMy dad's a doctor, so I know about the topic.
I think your question is kind of ridiculous, it's like asking if there is any way you could fly without wings after watching a Superman movie, it's a fiction movie.
Apart from that, there are some drugs that could help you concentrate, but there are NO drugs to STUDY, the drugs that "could" help you concentrate are drugs meant to realistic, mature purposes such as treating ADHD, hyperactivity, or other disorders.
Depending on the level of the illness, you'll be prescripted a stronger or weaker drug. I suppose you want to know about the strong drugs (Since you ask about Limitless).
The most famous strong drug that could be used to "concentrate" is Methylphenidate, comes in the names of: Ritalin, Aderall, Concentra, Rubifen (Spanish-speaking countries...) (Depending on how fast or slow the Methylphenidate releases into your body).
These drugs are drugs meant to be taken by SICK people, people that need it, and they are very strong and have VERY strong side effects (After all, we could say that Methylphenidate is an "amphetamine"). Some side effects? Growth stop, psychosis, triggering schizophrenia, heart problems, loss of lots of weight (and many others)... without forgetting the addiction effect (They are very addictive, just like in the movie).
I got a friend that used Ritalin to study for university. After finishing university, he got into a deep depression due to dopamine levels depletion and wouldn't even leave home for the entire summer (Plus all the side effects that it caused in him that will accompany him all his life).
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As I said there are no drugs made specifically for people to "study", but there are drugs that could be used to concentrate. Saying that, taking cocaine, amphetamines, or other similar drugs would also help you study.
In fact, Methylphenidate IS ALSO used as a recreational drug. People snort it and go to clubs or rave parties just as they do with cocaine and derivatives.
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And overall, if you did a trade-off between taking them and not taking them, the side effects (plus high monetary costs, since a doctor won't prescribe it to you if you're not sick), won't ever in the world add up to the benefit you get from them. The benefit you get is marginal, they might help you get a 2-5% more, that's it. The effort and hours on studying still has to be put.
And after all, if you asked a kid suffering from hyperactivity if he would still take Ritalin if he wasn't sick, he would, of course, say "never in the world".
Hugs! Quote if you got questions!