Medication can not cause an arachnoid cyst, unless it causes you to fall over and bang your head extremely hard then causing a collection of CSF to form on the Arachnoid Membrane.
Arachnoid Cysts are congenital, but they can also be caused by head trauma(which is how I got mine.) They are basically just obstructions of CSF flow. I had 11 brain surgeries because of mine.
Arachnoid cysts are developmental malformations in the brain, which usually remain asymptomatic even if the cyst is quite large. Hormonal imbalance has been thought to be causative but the role of medications has not been reported.
However, minor head trauma can damage the existing cyst, leading to some complications. This gives rise to symptoms of raised intracranial pressure and nerve compression such a headache, visual disturbances, seizures, weakness or paralysis on one half of the body) and loss of muscle control. Frontal arachnoid cysts have been associated with depression.
They are generally incidental findings on MRI scans. Some other tests could be mini mental state examination (MMSE) and cognitive questionnaires. Treatment is however controversial. There is difference of opinion among clinicians whether to treat only patients with symptomatic cysts or even asymptomatic patients also require treatment.
The treatment options may include anything from no intervention to surgical decompression to excision of the cyst to provide relief from symptoms. Hope this gives you some insight.