My dd was on it for about three years from year two to year four at school mainly for anxiety. All I can say is that within a week she had changed so dramatically she was unrecognisable, for the better.
CAMHS explained it to me as being a way of changing her behaviour so that she learnt new ways of doing things. So before she wouldn't talk to people, was terrified of noise, wouldn't go to any swimming events, even though she was the best swimmer in her year. I can hardly remember all the things that she was scared of but basically she wasn't joining in with life, she was watching scared from the sidelines.
After taking Prozac she joined in with everything, she was quite naughtly and lound and funny and bonkers and didn't care anymore what people thought of her. She was told off in school for some hilarious things. She went to a swimming club for trials and did the trials without clinging on to me and crying. She moved to a new school only knowing two other children and walked straight into the classroom without even looking back at us. She made new friends and talked to her teacher every morning about something. When she went on holiday she chatted to people on the beach and had a little gang of friends who followed her everywhere as she was the best crab catcher. She was also the best bug catcher in school and a group of other children followed her round the playground catching buts. My list could go on and on.
We decided to take her off after talking CAMHS said they didnt' think she needed it anymore as her behviour had changed so much. I was terrified, I thought she would regress and without the medication she wouldn't be able to function again. She was taken off it gradually over around four months and she became much calmer and the change was noticable, she was shy again but not terrified. She doesn't talk quite so much as she did but she will talk.
She also told me recently, as dd2 is also scared of many things and so I asked her why she isn't scared any more and she said that she realised that being scared wouldn't kill her and that she wanted to do things more than not do them because she was scared.
Also another thing that we had talked about with CAMHS is how high her level of anxiety would go. Basically it only goes so high and then plateauxs off and then comes down, but some children don't realise this they have to be taught. They believe it will just keep getting higher and higher and don't know how to handle this.
I would say that I am a firm believer that Prozac can works wonders. My dd was also on Ritalin and I wouldn't talk very highly of that. There is far more research done on Prozac than Ritalin and is seen as a much safer drug just very few people talk about it's use off label.