Are you sure Suprelorin is available in the US? I was looking into this stuff earlier this year and thought that the only chemical option for us is Zeuterin, which is permanent. The upside of Zeuterin is that it only reduces testosterone by about half, so you hopefully see some behavioral benefits without removing all of the health benefits of testosterone. However I decided not to do it as the technique hasn't been around long enough to know about long term health effects.
This topic is one I wrestled with for a couple of years. I feel that it's overall healthier to leave dogs intact (particularly males), however Cai has been intensely focused on dogs since he hit adolescence at 4 months on the dot. He became leash reactive *literally* overnight. His reactivity is almost entirely due to frustration at not being to run over and greet other dogs. There's also a small proportion of it that is alert behavior, that appears when he's off leash and a dog appears unexpectedly, but that seems to be a carry-over from practicing the frustrated reactivity so much.
Cai is also obnoxious around females, both spayed and intact. He obsessively sticks his nose right into their privates and needs strong corrections to be dissuaded. If the girl doesn't correct him, he follows her around non-stop. He's not often off-leash around females except when briefly passing on hikes, so I've just managed him with a leash when the situation's come up in the past.
I polled multiple trainer friends on this topic at ClickerExpo this past January, and they mostly agreed that neutering would *probably* help, but maybe not because he was 3 years old at that point and had had lots of practice at these unwanted behaviors.
A couple of months back I got a chance to meet up with Dr Amy Cook, and she provided helpful insight. She noticed that his reactivity included a lot of posturing, and I said that he also marks after every single reactive incident. Her analysis was that decreasing his testosterone would likely improve his intense interest in other dogs. That was what finally convinced me to neuter him, and he had the surgery two weeks ago. I will certainly provide updates as I see any change in his behavior. (I'm currently on vacation and will be picking him up on Tuesday. In the meantime he's gone from being a dog who will sometimes turn up his nose at his usual high-value treats even when we're at home, to devouring everything he can get his little teeth on. If the neuter changes nothing else, at least I'll have a dog who is easier to train on the food motivation front.)
But there's one more thing at play in this decision: trainer ego. When he was younger, neutering him seemed like taking the easy way out. I wanted to be a "good enough" trainer that I could work through the issue. I've certainly improved as a trainer thanks to him (and thanks to the training methods at FDSA, which think outside the box), but after 3.5 years (and an anxiety attack in front of everyone at Ferretpalooza), he's worn me down.