People medicine vs Pet Medicine what's the difference?

I had a cause to use some Immodium AD for my baby last week when he was sick with diarrhea. I generally don't use over the counter meds with the exception of benedryl  on occasion with the other furkids... I have raised/showed horses, cows, pigs, rabbits, dogs, birds, turtles and a cat here and there since I was 3 years old.  Many home remedies have been used during my 40 plus years and I didn't run to the vet for every little snafu.

Gunner is a change of life baby I think. I am more cautious with him, I am guarded with him, and I am acutely aware he is a 4 legged animal, however, he has restrictions that none of my other animals/mammals had.

When I took him to the vet, she said it was ok for temporary and gave me some stuff to use at home for now and in the future.  This sparked a huge debate. 

Many argue the medicine doesn't know where it's going. Dr. D was great she didn't say you shouldn't use it, she said temporarily it was ok. I believe she was shocked I would be so concerned, but I revert back to BullDogs are new to me, and  I had the poop scared out of me the day I bought him, even though I slightly researched (LOL)...

So to get an impartial opinion, I called upon my trusty semi-retired spoiled me rotten vet to give it to me straight so I could effectively explain and his response was priceless...

His first sentence of the explanation was "Vet's say not to use human medicine so they can charge you more for rx's that say Pets only"... He was clearly kidding and why I love him so much.

Then he explained as did Dr. D that there is no way of knowing how long "human over the counter medicine" lasts in a pet's system. How you dosed an animal, what is in the medicine that could react to the dog or specific breed (i.e. Australian Shepherds or any Shepherd breed have issues with some Pet Meds too, heart worm pills, blood issues)...

Never give aspirin or pain meds that we take, tylenol, motrin because it messes up their stomachs, so much I learned from Dr. D and my semi retired vet who has spoiled me rotten for 40 plus years...

Using the home remedies I know still work, and I needed to relax, using common sense and having a good dialogue with the Vet is paramount. 

So while everyone thinks I am crazy for not wanting to use the over the counter stuff on Gunner, in a pinch I may, but 99% of the time, I will default to the Vet.

I would hate to overdose my baby Gunner.