I started on Eglonyl after the birth of my daughter last year.
I did not need it, but requested it as I thought "well this can't do any harm" and I had only heard good things.
I had never had milk production problems, but I tend to solve problems before they occur, and my OBGYN had no problems with me taking them.
I did not really experience any side effects or issues.
I do however suffer from depression and maternity leave usually throws me to the bottom of the pit. I had my 3rd child in June 2009, and by July was seeking therapy and requesting anti-depressants as I was really struggling to cope.
My psyciatrist suggested I stop the Eglonyl - and said that though it worked well, I clearly did not need it and it would be better not to take it if I was going to take anti-depressants as well.
I went off it immediately, no side effects and my milk supply continued without any problems. I breastfed exclusively until 6 months and then introduced formula and the like.
My OBGYN also mentioned that if I need to come off it, I should just stop.
I did not have any negative effects from Eglonyl, and the abrupts stop, but I am sure there may be other moms who might have experienced negative side effects.
(I suffer with low libido and depression going in to it, so I cannot comment on whether Eglonyl made it worse or contributed at all ... I personally do not think it did.)