In a word? Yes. A "teacup" dog, such as a teacup Chihuahua or teacup poodle, is the same as any other member of her breed with one important exception: size.
When grown, teacup dogs weigh less than the American Kennel Club-approved standard weight for their breed, often by a pound (half a kilogram) or more. For example, if a Yorkshire terrier normally weighs 4 to 7 pounds (1.8 to 3.1 kilograms), a teacup Yorkie may weigh only 2 to 3 pounds (0.9 to 1.3 kilograms).
Why the weight difference? It's normal for some puppies to start life smaller than their littermates, earning them the dubious distinction of being the "runts" of the litter. These very, very small puppies may actually fit in a teacup, and some breeders are quick to market their "smaller is cuter" appeal (after all, the term "teacup" is much easier to sell than "runt"). Some even breed unhealthily undersized dogs together in the hope of creating more minis -- teacup puppies are sometimes sold for thousands more than their regular-sized relatives, a demand fueled by celebrities who tote impossibly toy-like dogs in couture purses.
Unfortunately, teacup dogs may be plagued by a host of health problems because of their tiny size. The risks include hypoglycemia (a potentially fatal drop in blood sugar), loss of sight, heart trouble, seizures and respiratory issues that can worsen with age. A teacup dog may not have enough room in her mouth for adult teeth to come in. Plus, her bones may be more fragile than normal. This means that her underdeveloped cranium may have a permanent soft spot, or her legs may be easily broken by a jump off the couch or zealous love from a child. And because she has a very small bladder, housetraining your teacup may be a challenge.
If you're considering adopting a puppy or adult that's a "teacup" version of any toy breed, make sure you get a certificate of good health from a veterinarian before you finalize the deal. A reputable breeder will offer a contract that includes a health guarantee; this agreement also may require you to have your puppy checked by your own veterinarian soon after purchase. Even experienced breeders may unintentionally end up with a smaller-than-average pup; however, they'll also insist the dog be spayed or neutered to ensure the ongoing quality of the breed.
To find a trustworthy breeder, ask your veterinarian or local breed clubs for referrals. When possible, make a short-notice visit to the breeder. You'll be able to tell whether the dogs are clean, happy and raised in humane conditions, view the puppy's parents and ask questions about the best way to transition your new charge to her life with you.
Or you could contact your local animal shelter or rescue group. Small breeds in particular are at risk for abandonment, sometimes because teacup dogs outgrow their pet parents' size expectations. You, however, could step in and make a big difference in a very small dog's life.