I looked up your first medication you mentioned, & here's what they say (this is just a very general info, though, from the Zyprexa site,NOT from a Doctor)...
This medication is used to treat certain mental/mood conditions (schizophrenia, bipolar mania). It works by helping to restore the balance of certain natural chemicals in the brain (neurotransmitters).
Some of the benefits of continued use of this medication include feeling less nervous, better concentration, and reduced episodes of hallucinations.
This section contains uses of this drug that are not listed in the approved professional labeling for the drug but that may be prescribed by your health care professional. Use this drug for a condition that is listed in this section only if it has been so prescribed by your health care professional.
This drug has been used to treat dementia-related behavior problems (e.g., agitation, aggression) when standard treatments (e.g., behavioral therapy, cholinesterase inhibitors) have not been successful.
This drug should only be used for the condition for which it was prescribed.
..."HOW TO USE:
Take as directed, usually once a day by mouth with or without food. Stand up slowly, especially when starting this medication, to avoid dizziness.
The dosage is based on your medical condition and response to therapy.
Use this medication regularly in order to get the most benefit from it. Remember to use it at the same time each day.
Inform your doctor if your condition persists or worsens...."
Hazy, as you can see by the above (brief) description on the site, your Doctor is really the only one that can let you know what you can or cannot mix with Zyprexa, and also, if any weird side-effects occur, you should call your Doctor immediately, so that you can discuss this.
I would think that discussing w/ your Doctor whether you can take Zyprexa with Ativan, is a must, since he/she would know best.