In Australia we have pellets as the default after 1-2 years; they're very stable, but they need to be surgically implanted, sometimes they get covered in scar tissue and don't work, and the decay in levels is linear over the whole 3-6 months they take to dissolve.

So you get a huge spike a month or so after getting them in, then a few months later your levels are bad but not bad enough to get a new pellet, then you spend a month being perimenopausal, then you get a new pellet if you're lucky (else you miss the pellet running out and get a T spike)