The one-year-old Bedlington Terrier was on her daily walk around Calf Heath Reservoir, between Gailey and Cannock in Staffordshire, when she went behind a bush and came across some discarded cannabis.
After eating it, Holly was left in a bad way and eventually threw up cannabis leaves, leaving her owner no choice but to take her to the vets.
David Williams, Holly's owner, said this isn't the first time an incident like this has happened and he wants to warn people in the area to be careful.
He said: "This happened four months ago when she was younger and she eat the end of a discarded joint.
"That time she was checked over and released with some tablets.
"This time she had to be given an injection and we were told to keep an eye on her overnight.
"Dog walkers need to be extra cautious down there, I won’t be going down there in the evening again."
David has reported the incident to the police and has also seen an increase in antisocial behaviour in the area and a large amount of CO2 cannisters on the floor.
A spokesman for Staffordshire Police, said: "Police were called at 9.16am on Saturday 20 November to the A5 Gailey at junction 12 of the M6 following reports of anti-social behaviour.
"A man reported that his dog had found and consumed cannabis left along a lane leading to Calf Heath Reservoir on 19 November.
"Police issued the man with safety advice and told him that the local council is responsible for removal of any waste products."
Local officers have been made aware of the issue and patrols in the area are to be increased.