Why Can't My Dog Operate Heavy Machinery?

Meet Sugar. She’s a five pound, half-chihuahua-half-something else that I adopted four months ago — officially classified as “teeny,” as far as treat sizes go. She’s somewhere between two and eight years old; she went through so many fosters that her paper trail is a bit murky. Her hobbies include licking nostrils, building dens out of blankets, and bullying dogs ten times her size.

She also has a heart murmur, and for that, she takes half a pill of enalapril and one-eighth pill of vetmedin twice a day, all mooshed up into a peanut butter treat.

But there’s something weird about her bottle of enalapril. Namely, it has some bizarre warnings printed on the label. First off, Sugar shouldn’t take enalapril while she’s pregnant. That one makes sense. The drug is also prescribed to people to treat high blood pressure, and it bears a black box warning — the most severe warning for FDA-approved medications — signifying that it could kill or otherwise harm a developing fetus.

But there’s another stern warning that doesn’t make much sense: Sugar isn’t allowed to operate any heavy machinery, especially not cars, while she’s on her meds.

That sucks, because now I have to do all the driving. No one at 1800PetMeds, the online pet pharmacy from which I buy Sugar’s pills, would explain why the warning label was there, so I set out on an investigation.

Enalapril is an ACE inhibitor. That means it prevents the body from producing something called angiotensin II that tightens blood vessels and subsequently raises blood pressure. So thanks to her enalapril, Sugar’s blood vessels stay relaxed and her tiny chihuahua heart doesn’t have to work as hard.

When people take the drug, it can cause kidney damage and dizziness, among other things, so it makes sense that maybe they should hold off on any road trips or forklift operation. But Sugar doesn’t even have a license, so why should she care? And how am I even supposed to warn her?

According to the American Veterinary Medical Association’s webpage, federal law dictates that all medications prescribed to pets need to have identifying information for the doctor, pet, and drug, and “cautions/precautions including milk and meat withdrawal times,” which seems more relevant to farmers than to chihuahuas. Either way, there are no guidelines on how those warnings should be framed.

It seems unlikely that the warnings are for me. Even though the dog and human versions of medications are often fairly similar once you correct for dosage, it’s not like someone with high blood pressure can just buy enalapril off the shelf if they promise that it’s for their dog. Even with online pharmacies like 1800PedMeds that make it so I can renew Sugar’s prescription without paying to see a vet, we still had to go get that prescription in the first place. And every refill requires veterinarian approval before it ships, so trying to game the system and score some heart pills would be harder than just visiting a doctor in the first place.

According to Dr. Jennifer Coates, a Veterinary Advisor with petMD, the answer comes down to whoever packaged the pills. She explains that because enalapril is also prescribed to people, the pharmacy that sent Sugar’s drugs to 1800PetMeds didn’t bother to create species-specific warning labels.

“Their system is set up for dispensing meds to people and spits out the ‘people warnings’ regardless of species,” Dr. Coates tells Inverse. “But really, it’s not incorrect. Your chihuahua probably shouldn’t be operating heavy machinery regardless of what drug he or she is on.”

Dr. Coates explains that because the human and dog versions of enalapril are so similar, there’s no real difference from using a pet versus a human pharmacy, as long as you’re willing to put up with some silly warnings. But she adds that in some cases, pharmacists for humans may not be aware of species-specific information that could impact the safety and efficacy of some drugs.

But what sort of labels would have come with Sugar’s enalapril if we got them from a pet pharmacy? Dr. Coates says it depends on the veterinarian, since they often serve as pharmacist as well. In that case, Sugar may have gotten some specific information catered to her exact diagnosis or possible symptoms — along with, of course, a warning to not operate heavy machinery.