Ten-month-old Aramis collapsed "twitching and unable to stand" after he was found chewing on a packet believed to contain a substance designed to imitate a Class-A drug.
The incident occurred on Kinnaber Beach, Angus.
Within 30 minutes of ingesting it Aramis was described as "spaced out."
Like in humans, "legal highs" can cause dangerously high heart rate and temperature rises in dogs.
Experts at animal rescue charity the Scottish SPCA said they had never heard of a previous case.
Aramis's owners rushed him to the Robson Veterinary Hospital in Laurencekirk, Kincardineshire, where he was detained overnight and given intravenous fluids.
Vet Ian Anderson said it was the first time he had seen a dog consume a new psychoactive substance (NPS), which will be banned under draft UK-wide legislation.
Mr Anderson, 51, said Aramis suffered "no long-term damage or effects".
He said: "He was spaced out - he wasn't able to sit down or stand up.
"He was twisting and turning and his heart rate was very fast.
"Quite a lot of the time we get dogs who eat things they shouldn't, but this is the first time I have ever seen a dog eat a legal high."
He added: "Fortunately, our client's fast action to get him medical attention meant we were able to treat Aramis effectively and he is now recovering at home but the experience was extremely traumatic both for Aramis and his owners who spent a sleepless night worrying he would never come home."
A spokesman for the Robson Veterinary Hospital added that there had also been reports that another dog owner had come across needles while walking their pet on the coast at nearby Inverbervie, also in Kincardineshire.
Scottish SPCA Ch Supt Mike Flynn said: "This is not an issue we have come across before and we are glad this dog was not seriously harmed."
In June last year, a police investigation was sparked when potentially lethal blue poison was found on the coastline nearby.
Aramis's owners have asked not to be named.
A puppy has become the first dog in Scotland to receive hospital treatment after eating a "legal high" on an Angus beach.