The first month is the toughest for people who give up smoking, but some withdrawal symptoms persist for six months, a study finds.

Researchers at the University of Vermont found the common withdrawal symptoms included anxiety, hunger, difficulty concentrating, a craving for cigarettes, weight gain and restlessness.Most symptoms disappeared after a month, but "increased weight, hunger and craving continued for six months in many smokers," they write in Archives of General Psychiatry. Nicotine gum helps ease symptoms, they say.