>

When ketamine was being used recreationally in the 90s, kids would tell one another that it caused brain bubbles and all kinds of myths. 
It turned out it was useful for depression and may assist in helping with myelination of damaged neurons. Not only that, but compared to other anesthesia, it's less taxing on the system - it doesn't cause the respiratory changes other anesthetics can or tachycardia, that sort of thing. It's a pretty remarkable thing.
So, assumptions are a difficult thing to really make. I think the brain bubbles myth was such an assumption. I'm not saying this stuff could be good, I'm just saying assumptions and drugs don't always line up.
Ketamine was also used specifically for recreation, not as a cutting agent. 
Xylazine appears to be used specifically as a cutting agent in opiates, so it's probably just a cheap as shit sedative, no one is seeking it out on its own. In animals it's used with ketamine, so it probably adds something ketamine doesn't cover - muscle movement, etc. They're likely not at all comparable. 
Xylazine is a Phenothiazine while Ketamine is classified as a general anesthetic.
I am not a doctor, I just like drug topics.
Picked a few choice paragraphs for info, this isn't the entire article.

More than 40% of street drug samples tested in Rhode Island contained the animal tranquilizer xylazine, according to a new analysis out of Brown University. It’s the latest sign that the drug, which causes sedation and can lead to skin infections and overdoses, is continuing to spread through the illicit drug supply in the United States.
Xylazine, often referred to as "tranq," concerns public health experts because it causes such heavy sedation, which can leave people exposed and vulnerable for long stretches of time. It’s not an opioid, so Naloxone — which can help treat opioid overdoses — doesn’t work to reverse its effects. Xylazine has become increasingly involved in overdose deaths in the U.S.
The drug was common recreationally in Puerto Rico and then started showing up in Philadelphia in the early 2010s, Shover said. For the last decade, it’s been mostly confined to Philadelphia, she noted. Over the past few years, it started appearing in other places — like in Massachusetts and New York City.

Anyone know more about this drug? Curious as to what the draw is considering it's not an opioid, is it something more like Ketamine? I'd have to guess a cheap, accessible drug like that could certainly do some damage, although not sure how many people would go with that over something like heroin/fent.