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Yes, I don't see a problem there. You can cut the tablet if you want.
This will make the dose 25 + 12.5 = 37.5mg.
Adult doses can be safely increased to 75 mg per day. This can also be increased to 150 mg in a day in refractory cases. However, I would advise that you follow up with your Doctor on this one. As for your question, yes, you can cut the Elavil in half with no problems.