Which calming supplements actually work for dogs?

Most calming supplements make vague claims backed by marketing, not evidence. The ones that actually have published research behind them work through three mechanisms: L-theanine promotes relaxation via GABA pathways without sedation, melatonin regulates sleep and reduces situational arousal, and dog-appeasing pheromone (DAP) signals safety through the vomeronasal organ. The biggest reason supplements fail isn't the ingredient. It's wrong timing, wrong dose, or wrong match to the anxiety type. A daily L-theanine chew won't help a thunderstorm phobia that happens once a month. A situational melatonin dose won't lower chronic baseline anxiety. Matching the supplement to the pattern is the whole game.