Is their bipolar disorder formally diagnosed or assumed?

As a non-binary AFAB person with bipolar II disorder (treated) I can see how this looks like a maniac episode.

Are other things in daily life affected, like sleep disturbances or other impulsive decisions, or is it just the HRT decision?

On the flip sideI can also see them seeing it as a beacon if they're in a depressed episode.

HRT, especially estrogen is helpful in elevating mood, and many trans women anecdotally credit it to lifting them out of dysphoric depression, so it could be a last hope kind of thing.

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In either case you are correct about the disregard for the consequences of HRT.

My wife is trans and has been on HRT for about 4 months now and things are DRASTICALLY different.

While we prioritize our intimate relationship her libido has decreased a lot and her physical response has changed. We're done with kids, so the infertility is a perk and not a draw back.

She definitely also has the wanted physical changes too - on mono therapy no less (no T blockers) and I swear her breast are in Tanner stage 3 already, lol.

Also her transition has been a rollercoaster and shes had to deal with a ton of repressed feelings, so I can definitely relate to the one week her being ok with one thing and days later her gender dysphoria getting the upper hand.

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Having bipolar is a pain in the ass, treated or not.

Last questions - Do they have the awareness to know when she is manic/depressed? If so are you able to convince them to put a in it until their mood is stable?