You really, really shouldn’t give your DNA to genomics companies like 23andMe or Ancestry. As the recent arrest of the Golden State Killer reminded us, these genetic databases are a goldmine for law enforcement. Catching serial killers isn’t bad, of course, but problems start to arise when, say, these genetic databases are used to target people for deportation. But in case you needed another reason why voluntarily giving your DNA to companies is a bad idea, on Wednesday the genomic-ancestry company 23andMe announced it was forking over its DNA data to the world’s ninth-largest pharmaceutical company, GlaxoSmithKline (GSK). The exclusive partnership gives GSK access to 23andMe’s database that includes the genomes of over 5 million people.

The agreement was pioneered by the two companies’ chief scientists, Hal Barron and Richard Scheller, who previously worked together at another drug company called Genentech. Indeed, the partnership is a sweet deal for both companies. 23andMe sold GSK a $300-million stake for the four-year agreement and GSK gets exclusive access to one of the world’s largest private genetic databases. Ostensibly, the genetic information is going to be used for “research and development of innovative new medicines and potential cures.”

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23andMe began by selling ancestry services that were based on its customers sending in saliva samples, but last year the Food and Drug Administration determined that its sequencing tests were accurate enough to sell customers reports about whether they had risks of developing certain diseases. This effectively opened the door for 23andMe to dive into medical applications of its rapidly growing genetic database.

When a customer signs up for 23andMe’s services, they have the option to choose whether or not they want their data included in future research trials. According to a blog post by the company’s CEO, Anne Wojcicki, customers can choose to opt-in or opt-out of studies at any time. Nevertheless, 23andMe says 80 percent of its customers choose to allow their data to be used in future research.

There’s nothing wrong with using DNA to develop medicines, of course, but problems start to arise when this medicine is then sold back to the public at exorbitant rates. As the infamous pharma bro Martin Shkreli demonstrated, pharmaceutical companies can and will make life-saving drugs prohibitively expensive to juice their bottom line.

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This means that 23andMe customers will, in effect, be charged twice for any potential “innovative new medicines” their DNA helps produce. The first time they paid for the DNA sequencing service; the second time they pay for the medicine that it helps create. A more equitable solution, according to Peter Pitts, the president of the Center for Medicine in the Public Interest, would be to pay 23andMe customers for their genetic data when it is used in research.

“Are they going to offer rebates to people who opt-in so their customers aren’t paying for the privilege of 23andMe working with a for-profit company in a for-profit research project?” Pitts asked NBC News. “When two for-profit companies enter into an agreement where the jewel in the crown is your gene sequence and you are actually paying for the privilege of participating, I think that’s upside down.”

Another alternative would be for 23andMe to partner with non-profit public programs, such as the National Institute of Health’s precision-medicine initiative. The NIH is trying to collect 1 million genomes to further research on personalized medicine. While this sample size can be difficult for the government agency to collect, it represents just one-fifth of the data provided to GSK.