Though some peppers are labelled as non-edible, there are no red pepper plants that are intrinsically poisonous. There are many species of peppers that are grown for their ornamental value as opposed to their value as a food or spice, but they are no more dangerous to eat than any other spicy pepper.
Ornamental Red Peppers
In the 1970s, botanists and gardeners took notice of the fact that chilli peppers could be bred to look more visually stunning, with more variety in colour and more prolific vegetation. Ever since, new cultivars of pepper derived from the chilli have popped up in the nursery market as ornamental plants. Cultivars come in many colours, including purple, orange and yellow, but red is still a mainstay for these ornamental peppers.
Marked as Non-Edible
When ornamental pepper plants are bred, often much of the pepper's flavour is lost, making ornamental red peppers bland and mostly useless as a culinary tool. In such cases nurseries may label the peppers as non-edible, ornamental plants. This can be misleading, because though the plants are not being bred for edibility, they are just as safe to eat as any other pepper plant.
Though there are exceptions, red ornamental peppers are almost universally bred from Capsicum annum, which also include more common edible peppers such as the bell pepper and the chilli pepper. Though some ornamental species of the pepper may look very different from a chilli pepper, they are essentially the same thing. Among the most common red ornamental peppers is the Christmas pepper. Like most other ornamentals, they are Capsicum annum and though rarely eaten, they are not dangerous to consume.
Ornamental red pepper plants can technically be considered non-edible or toxic if they are excessively spicy. Spicy peppers, ornamental or otherwise, irritate mucous tissue and cause a burning sensation in the mouth and throat. Many people seek this sensation when eating a spicy pepper, and often ornamental peppers will yield the same result. So what may be perceived as a less-than-positive reaction to an ornamental red pepper could render it toxic or non-edible, but only in the same sense that chilli peppers are non-edible.