Hi My Husband Has Got Nasal Pharengen. Cancer He's On

Hi my husband has got nasal pharengen. Cancer he's on morphene and other medication at moment, he's having really bad constipation at moment ,he's tryed laxido for past 3 days he finally got to go after 10 days, how long should he take laxido for? And when he does finally go to loo should he stop taking it, it seems to say take it for 3 days .thankyou