Crafting The Unwanted Elements of a World

I've been developing basically a magic system in which it is possible to either work with the forces of nature and bend them to your will, or to draw on primordial energy to break and reshape the natural laws. Just guiding what nature can already do is very reliable, but obviously limited in what is possible with it.
Breaking the laws of nature has basically limitless potential in what can be done with it, but it becomes almost impossible to predict all the countless factors that determine the exact outcome. In theory it could be hugely beneficial to improving everyone's lives, but in practice it always eventually resulted in large environmental disaster areas because it broke something critical for nature in umforseen ways.
General opinion is that no good will ever come from such magic and most religions condemn it, but there are always new people who think they figured out all the problems and can create wonders that will bring unimaginable prosperity and power. Most people think they are crazy, but there are always some who seem to be really doing well for the first few decades, and there are always people willing to believe that this time will be different.

 

So I am not sure if this would count but...
There is always the problem of "healing potions" or "healing powers". And to my knowledge, there is never any real side effects. I decided to take this cliche and twist it around and come up with something unique or not used as often.
In Cyrom, there is this ancient magic practice that heals deep cuts and/or wounds. However, this practice is very time consuming; even a simple lesion such as an arrow wound could take several hours or days. During a war (The Dark War), the practice was experimented to shorten the length of time it took to reverse the wound.
After much experimentation, they successfully shortened the time issue...but not without consequences. Basically this reversal causes the person to experience the pain in reverse. So if they were stabbed in the gut, the blade was twisted, and then torn out, that victim would feel all the pain again as if in rewind.

 

There is a wonderful moment in the game The Witcher 3. The healing potions available to the protagonist are tailored to people who have been heavily alchemically altered. The side effect to normal humans are extremely unpredictable. There is one situation where a healer is certain the patient will die soon and they can decide to try one of these potions. A possible outcome is that the patient survives, but with severe permanent brain damage.

Something that I considered, as something of a relatively minor side effect to a magic system based around spirits, is that witches and shamans improve their ability to sense spirits to a point where it comes to them unconsciously. They reflexively turn their head to sounds normal people can't hear, or avoid walking through spirits other people can't see. Their minds are perfectly alright, they can accurately distinguish between the physical and spectral, but they still start acting in ways that seem really eccentric to others.

 

I haven’t gotten into in my world in the books, because what healing exists hasn’t been from the POV of a healer, nor has there been much in fact. But, when healing it takes experience and practice, or as the healer utilizes Elemental Life/Spirit, they can accidentally use part of themselves to heal. This poses the issue of both taking on the wound or disease one is trying to heal, and in more severe instances, deplete their body in an unrecoverable way, while diminishing their ability to heal again. And of course, it could also get the healer killed.

Nobody runs around with healing potions, per se, but all Elemental concoctions tend to have side effects from addiction to overdosing to things more nasty.

 

I apply several things to it. I have people who can shatter mountains with punches, so not only do mountains get broken, the entire world's architecture was shaped by the fact. There wasn't much they could do, but due to it Eld has some very secure buildings and walls, enhanced by magic. Weather uses have affected everything and created as many problems as they solve. Coastlines have been rearranged and rivers rerouted with magic. Magical plagues connected to undead have come about and their are potions that can be quite addictive, as with the above. Mutants from magical experiments have lead to underground societies and the Corruption has created things like the monster peoples. Some of them, anyways.

Due to the nature of the world, magic can make things go wrong as often as it goes right. And it's part of how the Lich Wars came to be anyways.

 

Only the obvious thing of magic inflicting harm on the users—especially when the magic used is far greater than the human body can withstand. I've had characters take dragon magic. Apart from causing pain, it also caused other strange things to happen to them.