Symptoms of insomnia can be caused by or can be co-morbid with:

Use of psychoactive drugs or stimulants, including certain medications, herbs, caffeine, nicotine, cocaine, amphetamines, methylphenidate, MDMA and modafinil
Use of fluoroquinolone antibiotic drugs, see fluoroquinolone toxicity, associated with more severe and chronic types of insomnia[11]
Restless Legs Syndrome, which can cause sleep onset insomnia due to the discomforting sensations felt and the need to move the legs or other body parts to relieve these sensations.
Periodic limb movement disorder (PLMD), which occurs during sleep and can cause arousals that the sleeper is unaware of.