Drugs that improve long term memory may also affect the part of the brain involved in working memory.
There is a lot of research underway into medications that could help with memory problems. One class of drugs that's been proposed as memory enhancers increases the activity of an enzyme called protein kinase A (PKA) in the hippocampus. This is an important part of the brain for long term memory and learning.

However, researchers at Yale University School of Medicine have now found that drugs targeting PKA could have an adverse effect on working memory which is involved in, say, keeping a phone number in memory long enough to dial it. They looked at agents that increase PKA and found they have an inhibiting impact on the pre-frontal cortex activity in animals. The pre-frontal cortex is known to be involved in working memory. So while such drugs would benefit the hippocampus and long term memory, it would be at the expense of the pre-frontal cortex and working memory.