Happiness is a side effect of doing something that has nothing to do with it.
Doubts can produce positive side-effects - if you work toward resolving them.
Antidepressants can have troubling side effects and are addictive for some people.
No action is without its side effects.
Don't do something just for the money. Money is a side effect of persistence. You persist in things you are interested in. Explore your interests. Then persist. Then enjoy all the side effects.
Depression is a side effect of dying. (Almost everything is, really).
When I was a practicing alcoholic, I was unbelievable. One side effect was immense suspicion: I'd come off tour like Inspector Clouseau on acid. 'Where's this cornflake come from? It wasn't here before.
Enraging liberals is simply one of the more enjoyable side effects of my wisdom.
There are always potential side effects for every vaccine.