Phalaris toxicoses is caused by ingestion of Phalaris genus, most frequently bulbous canarygrass (Phalaris aquatica, reed canarygrass (P. arundinacea), paradoxa grass (P. paradoxa), and sunolgrass (P. coerulescens). It generally presents in one of two forms---as 'staggers' or as a 'sudden death' syndrome in horses.

Phalaris spp are drought-tolerant grasses that are found most commonly growing in pastures during the spring and autumn months. The plants contain a number of different secondary metabolites implicated to cause phalaris toxicoses, including indole alkaloids (N-methyltyramine (NMT), N-dimethyltryptamine (DMT), 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT)) and tryptamine alkaloids (Gramine) which can affect both cardiac and neurological function in horses.

Although outbreaks of poisonings have occurred worldwide, Australia has a higher prevalence of phalaris toxicity. Horses are at a greater risk of toxicoses when Phalaris plants are young and undergoing rapid growth. Soil cobalt levels have been associated with outbreaks.