Giving Duphalac is not addictive .
Too much laxative may cause diarrhea.
I would not prescribe laxative for 2 weeks unless it is not controlled by diet modification .
Weight loss due to laxatives can only occur if it causes diarrhea .
First line of treatment would be diet modification . plenty of vegetables and fruits and salads . .
Next Steps
i would advise you to modify the diet first and see whether constipation resolves . and if not responding to diet modification then only give duphalac syrup that too at night time only once with water and only for 1 week .
Health Tips
Avoid milk and bakery products like biscuits and cookies etc as they contain Maida which causes constipation . Last but not the least plenty of water