Is Phenegran addictive? My dad is going nuts!?

My Dad takes Phenegran 10mg for hayfever, but it also makes you feel drowsy and sleep. I have noticed him taking these tablets a lot, especially at night. My mun says he takes them even when he doesn't have hayfever. I took the tablets and threw them in the bushes in the McDonalds car park. My dad asked 'where are the tablets?' I felt bad and couldn't tell him the truth, but I feel it's for his own good. He went nuts going through the house looking for the tablets! He opened the medicine cabinet and took everything out then checked his room again and then checked the back rooms. Now he has Just left to buy another packet! Is he addicted?