Weight loss supplements are based on natural plant extracts and amino acids. Weight loss is achieved in various ways.
Fat burners work by increasing your metabolism, for example through the thyroid hormones. This can be achieved as simply as having a cup of coffee, but there are many supplements which achieve this in different ways.
Quite a list of amino acids including methionine amd phenylalanine tell the brain that you are full, and act as appetite suppressants.
Other natural herbs which have been used for thousands of years have been shown to prevent the absorption of carbohydrates, hence the name carbohydrate blocker.