Dozens of companies invite customers to swab their cheeks, spit into a tube, and find out which antidepressant is right for them.

Their products — pharmacogenomic tests — aim to predict how someone with depression will respond to medications based on that person's genetic makeup, sparing them from the trial-and-error that often comes with selecting an antidepressant. Some companies, such as Color Genomics, require that a physician order the test. But many testing products can be ordered by consumers directly. A handful have been FDA-approved, Live Science reports.

Though psychiatrists see the potential of these tests, many doctors warn that those on the market aren't up to snuff. They say that hundreds of genes may affect depression, and that studies demonstrating the benefit of these tests are lacking.

Depression is one of the most common mental disorders in the United States. In 2017, an estimated 17.3 million U.S. adults experienced at least one major depressive episode, meaning that they had a depressed mood and most of the associated symptoms outlined in the psychiatric diagnostic bible, the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), for at least two weeks. About half of those people received treatment with medication, according to the National Institute of Mental Health.

But in the best-case scenario, common antidepressants might take six weeks or more to kick in. More often, patients try several medications over the course of months, dropping some and slowly fine-tuning the dosage for others, testing treatment combinations with their doctor's guidance. Meanwhile, these individuals may suffer unpleasant side effects, such as dry mouth and weight gain. About a third of people with depression are treatment resistant, meaning that none of the medications that they try provide relief.

Genetic test companies, such as Neuropharmagen and GeneSight, promise to cut out the guesswork — for a fee of a few hundred to a few thousand dollars, according to the Washington Post.

Similar to genetic tests used to assess cancer risk, these products scan for genes that might alter how the body processes antidepressant medications. Some tests search for gene variants that affect how quickly drugs are metabolized, whether the person assessed may have adverse reactions, or whether they’re likely to respond at all. Others tests look at genes that affect how the medications are delivered across the blood brain barrier to their target sites.