Why do we sometimes feel guilty for things that aren’t our fault? Like getting strung out on antidepressants?

Guilt is not an inborn feeling like fear; it is taught. As part of our moral training, we learn about right and wrong and guilt. We seem to have a huge capacity for taking the blame for things that aren’t our fault, because we have a huge capacity to learn. The secondary feelings, like guilt, are learned behaviors.

Unfortunately guilt doesn’t seem to work as intended. Usually people who should feel guilty, don’t, and those who shouldn’t feel guilty, do.
Guilt is seen as a useful rearing tool to teach children right behavior. However, while guilt instruction is most intensive and effective with very young children, youngsters have the least capacity to understand it. They may be made to feel guilty for things that they don’t have the developmental capacity to control. Even when they are too physically immature to control bodily functions, they are capable of learning to feel guilty, which becomes a strong, nonspecific, feature of their emotional make up. They carry a deep sense of guilt for their perceived failures. And they will subsequently try harder and harder, making tasks harder than they actually are in later life.

People who have done nothing wrong are often wracked with guilt.
Guilt is supposed to be a motivator to act right in the future, but it doesn’t seem to work that way. It seems to be more retrospective—about the past. For instance, what mother wouldn’t feel a pang of guilt when she finds out she has been unknowingly feeding her child poison? Does she deserve self-punishment? No. Should she loudly and angrily direct the blame at Monsanto? Yes. Self-punishing guilt in this case serves no constructive purpose because the mother will switch the food anyway (without needing the guilt as a motivator). All it does is add to the suffering.
There doesn’t seem to be a good correlation between actual guilt and feeling guilty.

For instance, religions teach morality and guilt, yet some of those teachers are pedophiles. Pedophiles rarely feel guilt for actions that cause untold harm because they suffer from narcissism and other disorders which make it difficult for them to empathize with others.

Those who harm you would like nothing more than you taking the blame. Self-inflicted guilt for others’ actions takes the real bad actors off the hook. Taking the guilt on oneself ties their box of poison in a pretty pink bow for them so they can wash their hands of it. We shouldn’t do their expiation for them. Friends at IAWP: if you feel a pang of guilt, replace it with getting a present for yourself.