Interest groups are organizations or associations formed by people who have come together to achieve or promote a common interest. Although interest groups might look political, their interest can be anything aside from politics. On the other hand, pressure groups are also related to interest groups. They are often considered as a vital organ within interest groups. However, they are different from interest groups since they are created to address certain policy or political issues. If interest groups want to influence a policy, they will form pressure groups within themselves to mount pressure on the government so that the policy can favor them. Interest groups are organized hierarchically to designate responsibilities to members. The formation or organization of pressure groups is stricter. They also have some hierarchical arrangements in their organization. However, pressure groups as most times seen as lobbying firms or organizations. Some interest groups do not need federal regulations since they are not related to politics. On the contrary, pressure groups need federal regulations.
One of the reasons why people tend to confuse the two is due to the fact that pressure groups are also parts of interest groups. Their purpose may be a bit different though. When you say interest groups, this means that you are looking at the type of work that is needed for the development of certain causes that can be found in public. When you say pressure groups, from the name itself, you can already guess, that this means that you are trying to provide pressure to the public so that certain policies can become available. Take note that there are different subject areas that are available that can be handled with the help of pressure groups.