Well, actually, the answer depends on how you use ms-access.
Ms-access is really only the interface tool to a database. So, the database
part is not really in ms-access.
If you use a adp project in ms-access, then you do have triggers and even
stored procedures. So, depending on how you use ms-access, the answer will
vary.
Ms-access comes with two database engines. One engine is the MSDE, and it is
the equivalent of sql server. This engine has triggers and stored
procedures.
The other data engine is called JET, and when you use JET, you don't have
triggers. You can as others mentioned use the before update events in a
form.