Are hawthorn berries poisonous?
We know certain tree berries such as yew and laburnum are poisonous to humans, however, little is known about how poisonous hawthorn and other tree berries such as rowan and crab apples are. Given the fact that you can buy rowanberry jam and make wine from hawthorn berries and crab apples it is highly unlikely that they are very poisonous. In support of this there has never been as far as I know any reported case of hawthorn berry poisoning in humans that has resulted in death. Consequently, eating a small amount of these berries would probably have no long lasting effects on human health. Consumption of higher amounts of hawthorn berries may, however, result in a severe stomach upset.
