When smoking cigarettes was common, there was a lot of misinformation about how harmful secondhand smoke could be. As more data emerged, smoking bans emerged to protect workers, children, and anyone else who may be at risk. This is one of the reasons why cannabis is so regulated: to avoid exposing people to unwanted risks of second-hand smoke.
States that allow personal consumption typically only do so in private residences, prohibiting public consumption. There is one group that still faces the risks of secondhand smoke without having the ability to make the choice for themselves. Pets are often exposed to their owners’ second-hand smoke, and that is not really good for them. Animals’ threshold for cannabis tolerance is different from humans, and any exposure may be potentially harmful.
Is Cannabis Secondhand Smoke Safer than Tobacco
Multiple studies have been done regarding the harmfulness of secondhand smoke on pets, but most of the data are based on tobacco smoke.
The Centers for Disease Control and Prevention (CDC) points out that cannabis and tobacco smoke contain many of the same toxins, but in different amounts.  In fact, cannabis smoke has a higher concentration of multiple toxic particles, including significant amounts of hydrogen cyanide and more than triple the concentration of ammonia than tobacco. 
These differences may be negligible to humans, but animals have different metabolisms, cardiovascular, and digestive systems. Cannabis appears to be potentially more toxic to the average household pet. 
Pet owners should be concerned with cannabis smoke’s ability to permeate an entire house. One study found the concentration of fine particle matter (PM2.5) was 4.4 times higher in every room following cannabis smoking compared to tobacco.  Fine particles from smoke may lead to heart disease or stroke after extended exposure.  This means that even if the cannabis is smoked in a single room, pets anywhere in the house may still be at risk of exposure.
These data should be assessed with skepticism, though, because while tobacco is linked to cancer, the connection has not been established with cannabis. 
Since there is not enough long term data about cannabis exposure in pets, most veterinarians are focused on the short term risks of cannabis consumption.
Secondhand Smoke Risks for Dogs
Cannabis can be toxic for dogs, who are even more at risk than other common pets for two main reasons. Studies show that dogs living in smokers’ houses see higher incidence of allergies, respiratory issues, eye infections, and lung cancer. 
These represent a possible long term risk, but there are multiple short term risks as well.
There is No Smoke Without Fire
Over the last seven years, the number of dogs overdosing on cannabis has risen almost 450% over the last six years.  Anyone who has ever owned a dog knows that their curious nature means that they are prone to eat anything they can find. This means that edibles may not be a safe alternative for dog owners. Moreover big cities have also seen a 300% rise in dogs exposed to cannabis from eating cannabis butts. Even taking your dog for a walk may put them at risk if you are not paying attention. If a dog does consume too much cannabis, there are several signs to watch out for.  Smaller doses may lead to the following symptoms:
- Heart irregularity;
Cats and Cannabis Consumption
Cannabis is also toxic to cats, but the risks are different from dogs. The good news for cat owners is that 96% of veterinary visits due to cannabis exposure come from dogs, not cats.  When it comes to secondhand smoke, though, cats face a higher risk. Cat lungs are also sensitive to smoke particles, and one study found that cats exposed to secondhand smoke are three times more likely to develop malignant lymphoma than those who are not. 
The reason cats face a higher risk could be that because they are self-cleaning animals, they could ingest smoke particles trapped in their fur during grooming. 
Signs of cats exposure to cannabis are the following:
- Strange behaviors;
- Increased vocalizations;
- Loss of coordination;
- Loss of consciousness;
- Heart palpitations.
Small Pets and the Largest Risk
There is a reason canaries were used as an early warning sign for toxic gas in coal mines: small animals are even more sensitive to toxins in the air. Birds, mice, and rabbits all face higher risks from second-hand smoke than larger pets.  Part of the reason is that birds are more sensitive to airborne toxins, but also it relates to the size of the animals lungs.
The smaller the lungs, the more they are exposed to smoke because of the surface area to volume ratios. This may help to explain why pets overdosing on cannabis is rising for almost every species. 
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