Not a doctor or pharmacist so, layman's understanding. Each of the shots is designed to release it's dose into your body at a prescribed rate over the covered period. So, if you take the 90 day shot, it contains 22.5 mg which over each 30 days releases 7.5 mg into your body.

I don't know if there are any differences financially but given that there is a consult and nurse who administers it each time, the 1 and 3 months shots are going to cost more since there is a charge for that. If your mindset is less visits to your medical team the better or the commute is long, that may play into your decision. Another factor in your decision may be if you think you might stop the treatment and do something different because of the SEs, that may lead you to the one or three month shots.

There is an alternative - https://www.medscape.com/viewarticle/942933#:~:text=The%20US%20Food%20and%20Drug,oral%20gonadotropin%2Dreleasing%20hormone%20antagonist.

This does not have the flare associated with Lupron, has a lower CV profile, is "better" at keeping your T level castrate and quicker to clear your system once you stop. It does require self discipline since you must take it at home on a regular basis and depending on your insurance, may be more expensive.

Kevin