Motillium can be longterm. However, whether it's necessary is another matter. Motillium works by increasing your prolactin levels.
In the third trimester of pregnancy prolactin levels are at their highest. But progesterone produced by the placenta stops it from working. When the placenta is delivered your body starts making milk, driven by the high levels of prolactin. So early milk production is driven by high prolactin levels. Over time, the mechanism that controls your milk supply changes. Over the course of the first months your prolactin levels go back to a pretty normal/low level, but your baby's frequent feeding drives supply. Prolactin levels tend to peak about 30 mins after a feed. So, in the long run your prolactin levels don't need to be high. In the early days your prolactin levels may drop prematurely if you are separated from your baby (if your baby is prem or sick) or if are not able to feed the baby at the breast very often, or use a pump. She's only 5 months old now. It may be that later on after she starts solids at 6 mnths, you could try reducing the motillium. See how it goes. Some women (often mums who breastfeed adopted children) take motillium for the whole course of their lactation. The website Low Milk Supply -- Providing Information and Support to Breastfeeding Mothers has some good inormation