It's often very effective, animals suffering anorexia and/or total lack of appetite, start eating very well after low doses of mirtazapine.
I'm just wondering if this could be useful to sick piggies too.
That's true, but rather sleepy piggie than a starving piggie ;)
Dogs are dosed usually once a day, cats only twice a week with very little dose (1/8 or 1/4 from 15mg tablet).
I'm very interested to know if this could be used in guinea pigs.
Diazepam (given intravenously, intramuscularly, or by mouth according to Harkness and Wagner) is one of several drugs that can be used to stimulate the appetite. Diazepam (also known as Valium) can encourage eating within a few minutes and will last up to a half hour but also causes sedation and ataxia [loss of coordination of the muscles, especially of the extremities].
Cyproheptadine (Peri-Actin 4mg - 1/8 pill, twice a day) has been used as an appetite booster by some vets.