Does clonzazepam cause short term memory loss even if you just take it as needed?

Yes: Klonopin (clonazepam) is in the family of medications (the benzodiazepams) that have properties which can depress central nervous system processing of information. Short-term memory is such a process that can be affected even by the use of "as needed" klonopin (clonazepam). This is a side effect that is often dose related; consider talking to the healthcare provider who recommended Klonopin (clonazepam) to review a dose amendments.

Yes it can.: It can depend on what you mean by "as needed." Clonazepam can cause sedation and it is not unusual for someone taking it to not be as alert, and for their brain to not process what's going on around them in exactly the same way, thus making it difficult to retrieve memories when called upon.