A monopoly significantly impacts consumer surplus, which is the difference between what consumers are willing to pay for a good or service and what they actually pay. In a competitive market, numerous firms drive prices down to the level of marginal cost, maximizing consumer surplus. However, a monopoly disrupts this balance due to its unique ability to control market prices and output.

In a monopolistic market, the single seller sets a higher price than would prevail under perfect competition, producing less quantity. This price increase and reduced output shrink consumer surplus. Consumers end up paying more for less, leading to a welfare loss known as deadweight loss. This loss represents the economic inefficiency created by the monopoly, as some consumers who would have purchased the good or service at a competitive price are priced out of the market.

Moreover, monopolies may engage in price discrimination, charging different prices to different consumers based on their willingness to pay. While this can increase the monopolist's profits, it often reduces consumer surplus further by extracting more of the consumer's willingness to pay.

Overall, monopolies reduce consumer surplus by setting higher prices and limiting output, leading to decreased consumer welfare and economic inefficiency. The reduction in consumer surplus highlights the adverse effects monopolies can have on market efficiency and consumer well-being.