Some years back, Reaves and I were going to do a book featuring a scientifically-made werewolf. I went up Pill Hill in Portland, hit the medical library, interviewed a bunch of doctors, from dentists to endocrinologists, and came up with a way of doing it using known science, and one not-so-huge suspension of disbelief.
With one thing or another, we didn't get around to writing the book. In a recent discussion online, the subject came up, in a conversation about vampires, and I thought I'd offer my how-to-make-a-werewolf as an exercise in research ...
First, the caveat: The creature had to be created without magic, even though we could use some of those tropes if we could figure out a way.
So, armed with this, I set out, and was able to come up with a scenario that was fairly simple, once I had the notion. It involved combining some things that, while not likely, could be stretched enough to seem possible.
Pretty much, you could do it with hormones and drugs.
Hormones are potent chemicals, and under the right tweaking, could be made to accomplish almost all of the classical werewolf features. Add in a few known drugs ...
Jo-Jo the Dog Faced Boy and Lionel the Lion Faced Man, were certainly hairy enough, examples hypertrichosis. Genetic in these cases, but the medical literature has examples of people who suddenly sprouted hair, and a combination of hormones and drugs could do the trick.
Third-set dentition -- extra/super-numerary teeth -- are rare, but do happen, and there might be a way to encourage this.
Drugs and hormone storms can make somebody fantastically-strong, fairly impervious to pain or less than crippling injuries, and full of rage. Angel dust, Roid rage, amphetamines, narcotics, easy stuff here -- make them time-release via some kind of implant.
An allergy to silver? Not impossible ...
Now technically-speaking, Larry would be no more related to a wolf than you or I -- he'd just be a hairy, toothy, bad-tempered, strong human, but he would look the part and be able to act it.
The limits: First, it would take a while to change Larry into Wolfie. Months -- and even if you fudged this a little, you couldn't do so by much -- hair and teeth take time to grow. Call it six months, you can get away with it, but much less than three or four months, probably not.
Second, once changed, Larry isn't going back on his own. You could shave or depilate the hair, pull the teeth, get the implant out and he might eventually come to look something like he did before, but the hair and teeth are the easy part; balancing the hormones would take weeks or months. That's not counting the repairs his body would have to make to injuries because it didn't throttle down while leaping about -- torn this, cracked that.
Be a lot harder to make a vampire. You could come up with sunlight allergies, somebody who drank blood -- though the nutritional aspect of human blood simply isn't enough to keep somebody alive and healthy. Chemicals for strength would work, but the blur of super-speed and the ability to spider up and down walls or fly would be a tad beyond current science ...