Hello, I'm Dr. Deb. I'll do my best to help you today.
I'm sorry for this concern for your dog but this actually happens more often than you might think.
Unfortunately there are no specific antidotes that can be given to reverse the effects of marijuana if a sufficient amount was ingested to cause signs. It takes about 1.5 grams of marijuana per pound of body weight to be fatal so toxic
doses aren't usually something we have to worry about.
However, if he/she ate it within the last hour or so, you can induce vomiting if you have 3% hydrogen peroxide on hand.
The dose would be 1 teaspoon for every 5-10 lbs of body weight in some bread. Walk her/him around and repeat the dose if necessary. Not all dogs will vomit although most of them will.
If you're unsuccessful in getting him/her to vomit or it's been longer than 1 hour, then whether or not you'll see any abnormal symptoms depends on the concentration and amount ingested.
Signs to monitor which usually start to appear 3 hours after ingestion include: incoordination and stumbling. Many become quite lethargic while others may experience hallucinations. Heart rates can go down and pupils can become dilated.
Some dogs will vomit on their own.
Some dogs actually need to be hospitalized if the signs are severe enough but most dogs will recover within 24 hours if a small amount was ingested. However, having said that, signs can last up to 4-5 days in some patients.
You basically have to wait it out and make sure that he/she doesn't hurt him/herself and is safe until the drug leaves his/her body.
I hope this helps. Deb