Regarding our products to help you in your situation, I can recommend BECOOL.
This product does not 'put your horse to sleep' or does not affect the performances at all, it just helps him relax his body.
It contains Tryptophan, an amino acid essential for the stress regulation, as well as magnesium, passiflora and camomile.
It is liquid as well, you can mix it to your horse's food, 30 to 60ml per day during 2 to 4 weeks. The quantity can be adapted to your horse's reaction to it.
You can give it as well around 4 hours before a stressful situation to come for your horse (travel, show...).