Medications
Many kinds of prescription and OTC drugs are known to cause insomnia. Examples include psychostimulants, cholinesterase inhibitors, antidepressants, statins (for cholesterol), and ADHD medication. Statins, for instance, have muscle pain as a side effect. This returns us to the early mention of physical pain making it difficult to fall asleep.
On the other hand, those of ADHD medications or even migraine OTCs can develop insomnia because many ingredients in the drugs are stimulants. This is especially true if the medications are taken in higher dosages throughout the day or in the evening.
