What is the effect of advertisement on monopolistic competition?

There is not much need for adverticement when one company has a monopoly over one product. It is only needed to remind the people this product exists and where they can buy it. There is no competition if you have monopoly.

If the product is coveted/needed/multiuseful usually one session of adverticing can result a rush to the store. This happened during war when there was lack of mostly anything. If you adverticed 'we have bread' you would advertice in a few moments 'we do not have bread'.