system
Given the following post, respond as if you're commenting on Reddit:
human
[Dune] Are there any negative side-effects to spice use?

The spice melange is often described as a drug and a narcotic. But other than the fact that withdrawal can be painful to the point of being lethal, I don't recall any negative side-effects being mentioned (and lets assume at this point that "prescience actually kinda sucks" doesn't count as "negative"). 

So, are there any, or is it purely beneficial so long as you have a constant supply? 

EDIT: I guess you can overdose on the thing and too much exposure can mutate you, but lets ignore those for a while, too.
gpt
The addiction and mutations ARE the only side effects and both so severe you can't put them aside as ignorable.
I don't think it's possible to overdose on melange, after all navigators lived in tanks full of gaseous spice.

The drug was cripplingly addictive and missing your dose meant death. Given that its a hard to obtain drug for those that aren't ruling class or navigators thats as big a downside as you can get.

Those that did get a constant supply mutated mostly eyes changing colour but navigators mutated so badly that it was rare for anyone outside of teh guild to ever see one.  They ended up being sluglike fish-men with v shaped mouths and no nose.