Traditionally, constipation is thought to be caused by diet that is low in fiber and high in fat. Along these lines, it is less likely to be the popcorn itself (which contains a fair amount of fiber; 3.6 grams in a 3 cup serving) but more likely the butter on them (or other sources of high-fat, low-fiber foods in your diet) that is causing your constipation. Other foods to watch out for are: ice cream, cheese, processed foods such as potato chips, frozen dinners, mashed potatoes.
Before you consider laxatives, consider adding the following items to your diet to help prevent constipation:
-plenty of water (at least 6-8 glasses daily)
These changes should be tried before laxatives, as laxatives can have some adverse effects on bowel function even long after taking them, can cause electrolyte abnormalities, or dehydration. If you do want to try an over the counter supplement, I would recommend a stool softener such as colace. I would also recommend an appointment with your primary care physician
to review your diet in more detail, and to help tailor changes specific to improving your constipation. If the constipation is severe, consultation with a gastroenterologist
should be sough.