Lotte Group founder Shin Kyuk-ho is taking medication for dementia, his eldest son admitted Tuesday.

A close aide to the chairman confirmed that the nonagenarian was prescribed Aricept in 2010 to treat his dementia.

Shin, who is embroiled in an ugly struggle for the vast Lotte empire between his two sons, recently refused to complete tests establishing whether he needs a legal guardian.

Aricept improves memory and cognitive functions and is used to treat Alzheimer's disease or cardiovascular ailments.

The aide said the founder has also been taking the sedative Stilnox to treat the insomnia that is among the side effects of Aricept, but this has led to sleepwalking, which in turn requires Seroquel, a medication for bipolar disorder.

So far Shin Dong-joo, the eldest son, has claimed that the founder is fit to manage the Korean-Japanese corporate empire, which would make him the chosen successor. It is unclear what brought about the volte-face. The empire is now managed by younger son Shin Dong-bin, who has the backing of shareholders and executives.

There was consternation among some Lotte executives, who feel it is disrespectful to the patriarch to reveal what medication he is taking and how far his mind is gone.

