I would reconsider my opinion here.
When the woman uses hormonal contraceptives, neither the man nor the woman can require the debt. That much is clear. Even if it is taken for medical reasons.
About things that reduce fertility, and are not also abortive, like hormonal contraceptives, things are not so clear.
As the experiments are only animal and not human, and the reduction in fertility is not scientifically certain in humans, and not over 90%, as in hormonal contraceptives, I would say that it is not a sin to use it.
Otherwise, it would be necessary to make a comprehensive research about anything we ingest. It sounds rather absurd to me.
I am obviously no expert, but using logic can go a long way.
If the couple uses it with the intention of reducing fertility, it would probably be only a venial sin, in my opinion.