So this just showed up as an ad for me. Don't know what algorithm put it there, but wtf.
Do yall know what this stuff is. It's an antibiotic. I (and many others) was prescribed this for the first 90 days I was in Afghanistan to prevent malaria. Other times I've seen it used was for when people were exposed to highly pathogenic bacteria while necropsying sick animals. Other uses, to treat venereal diseases caused by bacteria.
What I'm saying is, this stuff can really mess you up. It doesn't target a specific single bacteria, it indiscriminately wipes out many bacteria it comes in contact with.
Now, that may seem good right, kill the bacteria causing whatever, but there's a reason antibiotics are for a relatively short term and require a prescription. Not only will it kill the "bad" bacteria, but it will also kill off a lot of your "good" gut microbes, which is really bad in the long-term. We're in a pretty symbiotic relationship with our own microbiota. If you've ever been prescribed antibiotics, you've probably experienced the effects of killing off all the bacteria in your GI tract i.e. diarrhea, malaise, maybe some depression, and a whole host of other side effects. That's because you don't have the "good" bacteria helping you with your digesta. You're not getting all of the nutrients you'd normally get because your ingesta isn't getting fully broken down before passing through you.
Another downside of killing off all of these bacteria, they provide provide an immunologic barrier for you, meaning they have established populations that require resources to sustain themselves. Having an established microbiota makes it harder for a new "bad" bacteria to establish itself before the immune system can mount a strong response because they have to compete for limited resources with a strong well-established gut population. This is one of the main reasons yogurt is a suggested post antibiotic food, it has those good bacteria in it and it helps to reestablish a good gut microbiota. If you wipe everything out though, this provides the bad bacteria with a chance to take up residence and potentially make you VERY sick or even kill you.
Finally, this seems like it'd be a pretty unsupervised deal. We already have a problem with antibiotic resistance from people not following through with a complete antibiotic regiment. Can you imagine what can happen if a bunch of people are taking this, experience the side effects, and then stop taking it. It'll make stronger, more pathogenic bacteria that will cause a lot of harm.
What I'm saying with this is, please be careful with what you're buying online. While low dose doxy is a treatment, it'd be in your best interest to consult with a dermatologist in person to verbally discuss your options.
TL;DR version: doxycycline is an antibiotic that's used for a lot more than just acne.
Taking it without first consulting a doctor can lead to much more harmful effects than clearing up acne.