Gabapentin 100 mg is a prescription medicine used mainly for:

It is commonly started at a low dose such as 100 mg, particularly in older adults or people with kidney problems. Take it only in the schedule your prescriber gave you. Do not increase, share, or stop it abruptly.

Common effects: sleepiness, dizziness, tiredness, unsteadiness, blurred/double vision, nausea, and ankle or leg swelling. Avoid driving, alcohol, and sedating medicines until you know how it affects you. MedlinePlus drug information and NHS side-effect guidance advise gradual dose reduction rather than suddenly stopping it, because withdrawal symptoms and, in people treated for seizures, worsening seizures can occur.

Get urgent help now for trouble or shallow breathing, blue lips, extreme sleepiness/confusion, facial or throat swelling, or a widespread blistering rash. The risk of dangerous sedation or breathing problems is higher if combined with opioids, sleeping tablets, alcohol, or other sedatives.

If you tell me why it was prescribed, your age, and the instructions on the label, I can help explain how it is usually taken and what to watch for.