Blue was enjoying a walk with his elderly owner when he sniffed out a bag of heart-shaped pills and started eating them from a plastic bag.
The horrified owner, frightened that a child may find them, took the bag and his 17-month-old dog home.
Before long, Blue became unsteady on his feet and started foaming at the mouth.
The owner contacted the PDSA charity and Blue was rushed to the Pet Hospital in Bradford where he was given emergency treatment.
PDSA head nurse Miriam Wilson said: “When Blue arrived, his condition was critical.
“He’d collapsed and the toxins were causing organ failure.
“He was admitted and life-saving treatment was started straight away.
“He was put on an IV drip and received activated charcoal to absorb the toxins.
“Without the treatment, he would not have survived the night.”
Blue has made a full recovery and is now back to his lively, former self.
The incident was reported to the police, who came and collected the drugs and disposed of them safely.
The owner has asked to remain anonymous.
The PDSA warned owners to get their pet checked out quickly if they appear to have eaten something harmful.