Ketamine is very variable in terms of side effects depending on the doses you use. I doubt it would be good for long term use but acutely it is awesome because it remains cardiovascular stable so it's great for trauma patients who have lost loads of blood, it's a bronchodilator so it's great for asthmatics and you don't have as much respiratory/airway loss like other anaesthetic induction agents. But that is all from a general anaesthetic dosing point of view.

At lower doses I've used it for dressing changes on burns patients and for manipulating kids dislocated limbs. You give a small dose, wait for them to go into a sort of fugue state and then pop the shoulder back in.

It is associated with the potential for profound hallucinations and increased salivation though. It provides a dissociated consciousness. One patient described it as like he was watching what we were doing to him as if it was like watching a TV show. No pain at all but it didn't feel real. Some hate that feeling, some don't care.

Again though I suspect long term use, which I am not familiar with,comes with side effects and problems.

Nerve blocks can last between a few hours and a full day. Depends on what you use, where it is used and how much. But it's labour intensive. Not really something that can be done every day. Plus there is alway the risk that the needle causes damage to the nerve if the person isn't careful with it.

A few places for chronic pain give IV lidocaine infusions. You come in for a few hours, get the infusion with monitoring. Then go home the next day. Again labour intensive and so often the funding isn't available to have it in many locations.

The best therapies in terms of long term benefits are usually physiotherapy and psychology. Ultimately if a pain becomes a chronic pain, the neural pathways alter and essentially don't work how they should do. Therefore removing the pain entirely often becomes impossible and those two therapies help the most because they help the patients accept and deal with the pain so they can get on with life. Unfortunately many patients are unwilling to accept this reality and believe there is a magic cure, a silver bullet, a perfect pill that sorts everything out.