Known as the "smart pill," or "study pill" in South Korea, the number of patients prescribed methylphenidate, an attention deficit hyperactivity disorder treatment, has seen a dramatic increase in the first half of this year, a new report found.

According to the Ministry of Food and Drug Safety, the number of people prescribed this ADHD treatment during the first half of this year -- some 257,000 -- reaches nearly the same number of prescriptions for the drug made all of last year.

The figure is about 90 percent of the over 286,000 patients who were prescribed methylphenidate last year.

Methylphenidate is a medical narcotic that stimulates the central nervous system and increases alertness.

It is used to treat ADHD, a psychiatric disorder characterized by symptoms such as attention deficit and hyperactivity in children and adolescents over the age of six. But experts have warned of excessive use, as it can cause side effects such as headaches and insomnia, and in severe cases, hallucinations, delusions and suicide attempts.

The number of prescriptions for teens and younger is also increasing dramatically. In the first half of this year, 85,106 males aged 19 and under were prescribed methylphenidate, the highest number of patients by gender and age. Some 90,851 males aged 19 and under were prescribed the drug during all of last year.

There were a total of 32,780 prescriptions for female teens and younger in the first half of this year, followed by women in their 20s at 35,773. This figure is also close to the 34,888 and 39,201 prescriptions recorded last year by girls and women in the same groups, respectively.

In addition, in the first half of this year, 28,508 men in their 20s and 26,300 men in their 30s were prescribed methylphenidate, while 23,816 women in their 30s were prescribed methylphenidate.

The ministry said the sharp increase in methylphenidate prescriptions is "believed to be due to increased patient access to mental health clinics," but added, "the exact cause is being analyzed."