…or are laxatives just marketed more heavily towards women?
Also, yogurts that are marketed as “supports healthy digestion,” such as Activia, are marketed toward women.
Is there a fundamental difference between the digestive systems of women vs. men? And if so, are those differences present in children (that is, are girls’ digestive systems different than boys’)?
The menstrual cycle affects the digestive system in various unpleasant ways. The hormones that are released, estrogen and progesterone, can cause constipation, gas, bloating, etc.
For most families women do most of the shopping so I think they are just targeting potential buyers.
I meant to add another sentence here: Whatever Activia does (if it does anything at all), does it do for men, too?
I think this is it.
Yes, it works for men just as well as it works for women. 
Read up on probiotics.
I’m sort of worried about what form a commercial for “A MANS LAXATIVE” would take.
Either you’d be advised to already be seated on the porcelain throne before you even take it, or … it will still be marketed towards women for the reason already offered by dolphinboy.
I laughed, but I think this might legitimately be part of it. It’s an indelicate issue, so female-focused marketing might be a way they’ve found to make ads that don’t seem crass or overly clinical.
To borrow a line from Florence King, a laxative marketed to men might be called “Get Out Of My Way!”.
“GRUNT, The Mans Laxative. Because if you didn’t GRUNT, it doesn’t Count.”
Another approach: “BLAST-LAX: For the man on the go.”