Nobody like fleas or ticks—and not just because they’re annoying. They can spread dangerous diseases as well. But knowing which flea and tick preventative is safe for your pet is important, because these medicines can have serious health consequences.

Start by asking your veterinarian to recommend a safe and effective product instead of choosing one on your own. Then discuss administration details before applying any product to your pet’s skin—particularly if your four-legged friend is very young or old, pregnant, or nursing, or is taking other medications. Never ever use a dog product on a cat, because some ingredients are toxic to cats. And make sure you use the dose per weight as recommended on the package.

After you’ve administered the product, be sure to watch your pet for any side effects. If you notice anything unusual, contact your veterinarian right away.