The growing use of so-called smart drugs is a concern, government health advisers have said.
The Home Office has told Newsbeat the Advisory Council on the Misuse of Drugs is to carry out a review of their use.
Some users of the drugs, which are legitimately prescribed for brain disorders, say they can help them stay awake longer so they can study.
Health experts say side effects can include psychiatric symptoms, prolonged anxiety and digestive problems.
The most common smart drug is Modafinil, which is meant to be used to treat narcolepsy, a rare but serious brain disorder that causes a person to suddenly fall asleep at inappropriate times.
It's not illegal to buy prescription-only drugs such as Modafinil but it is against the law to supply them, or sell it on to others.
But it has been linked to the "smart drug" craze - where students take it to stay awake for longer and boost their concentration.
Ritalin, used to treat Attention Deficit Hyperactivity Disorder (ADHD), is also known to be used as a smart drug but is categorised as a class B drug if not prescribed. Possession can lead to a five-year prison sentence.
Smart drugs are often bought online on sites hosted outside the UK.
Andrea Petroczi, a professor of Public Health at Kingston University, says there is little evidence that suggests taking them actually makes people more clever.
"It's not a magic pill," she said. "It doesn't work without putting the work in, it helps you to put more work in."
Keeping you awake
Modafinil is a stimulant and works by preventing excessive sleepiness during waking hours.
The NHS says that there are many users for whom it is not suitable, including people with behavioural problems.
Other side effects include headache and problems going to the toilet.
Professor Kevin Fenton, Director of Health and Wellbeing at Public Health England, said: "Public Health England is aware of anecdotal evidence of some students misusing prescription medicine, often bought off the internet, and other wakefulness-promoting drugs to enhance their study and academic performance."
Jack Rivlin, 24, is the editor of student paper The Tab in Farringdon, east London, told Newsbeat he had bought some tablets on a foreign website during the exam period and says the tablets helped him get through revision.
"It's kind of like putting the rest of your life on hold for the purpose of work," he said. "You're not socialising.
"You might snap at someone and I remember my girlfriend at the time thinking 'I don't want to be around you when you're on it'."
The Tab questioned more than 1,800 students in an online survey about smart drugs and almost one in five of the respondents revealed they had taken "smart drug" tablets including Modafinil.
The survey was self-selecting so it's not a reflection of the UK student population as a whole.
Jim McVeigh, from the Centre for Public Health, a research centre specialising in substance abuse, said: "There are a number of different concerns.
"One is the long-term use of a stimulant and the problems [with that]."
He said that when buying off the internet it was difficult to know exactly what you are getting: "The benefits people may get off these are probably similar to high doses of caffeine but we do know the effects of caffeine.
"We don't know the effects of these drugs."