"cause not only" is a correct and usable phrase in written English.
It is used to introduce a new reason or explanation that builds on the previously given one. For example: "I decided to take a break from school cause not only was I feeling overwhelmed, but my grades had started to slip as well."
'Cause not only did he go out and solve the crimes, he came home and wrote it all down.
In vain, Church pleaded the Greek cause not only in London but at the Congress of Vienna (1814 15).
"Violent and abusive experiences can cause not only physical harm but can also undermine people's attempts to seek help and move on from homelessness.
"These documents, often speaking of concepts such as morbidity and anti-selection, could cause not only confusion, but also unnecessary alarm to the layman policyholder".
It would cause "not only uncertainty about the status of particular voting procedures, but also general frustration with and distrust of an election process changed on the eve of the election itself".
Some recent research suggests that low levels of serotonin in the brain cause not only sadness but also hostility, and that some heart patients could benefit from drugs used to treat depression.
High heels have been fashionable in the United States for decades, even though they can cause not only serious foot problems but knee, pelvic, back, shoulder and even jaw pain.
warning: Dragging a small car underneath your new S.U.V. could cause not only irritating noises but also friction between the S.U.V. and the road, which may slow you down.
He has far less day-to-day influence now, after years spent developing a theory he calls "socionomics," which holds "social moods" as the cause not only of market cycles but also of economic and political events.
They worry that a huge and well-aimed eruption from the Sun would cause not only the lights to go out, but would also damage transformers and other critical components of the grid.
Viewed another way, the history Singer cites reveals that mankind's innate attachment to violence is such that it finds cause not only in anger that is reasoned, but where it doesn't exist.
