Is it better to use hot or cold compresses for back pain caused by the sciatica nerve?

Sequence it : If acute, use cold to decrease inflammation and swelling. If after 48 hrs, heat will relieve the problems and loosen the muscle tightness in response to the nerve inflammation. However, this is merely transient symptom relief and does not last. Many meds available to improve discomfort level. Physical therapy, and/or exercise may help from the get-go. Some articles praise osteopathic omt.

Hot or cold: Sciatica is often accompanied by muscle spasm—or may even be a result of it. Cold tends to cause muscles to tighten more; so pain may worsen. Moist heat penetrates & relaxes tense muscles & increases blood circulation; so used in combination with nsaids (anti-inflammatory) &/or other analgesics should provide relief. Stretching muscles &/or massage therapy helps, too.

Either?: However, it will be temporary as it takes a lot to get down into the spine which might not work. Sounds like you have a pinched nerve in your back. I would suggest seeing a pain/spine specialist to evaluate you further to evaluate what level and what can be done to treat you. There are interventional treatments besides medications and surgeries that might reduce or eliminate the pain altogether