Addiction or over-dependence on smart drugs can become a genuine problem. If people take stimulant drugs they may unconsciously develop the former issue. That’s why it’s impossible to buy them over the counter without a prescription. However, many users don’t realize this before they obtain them.
It’s also possible to become dependent without addictive cravings. After using smart drugs a tolerance may develop over time. This means that it will ironically become more challenging to focus without using them. It’s also likely that users will take more to regain the same effect (via The Woods At Parkside).