I have suffered from the problem of a frozen right shoulder. When I say "suffered" I am conveying what a really horrid, painful experience it was! The pain is really horrible at night. Literally, my shoulder felt like a stone, the whole arm would become stiff & I constantly woke up to sit and get the circulation back. I have spent months of sleepless nights like this! I did not feel the pain during the day as much, only when I exerted it too much, but dressing is very tough with a frozen shoulder.
A frozen shoulder occurs when, as explained by my doctor, the shoulder muscles stiffen due to a contraction of the shoulder capsule. There is no outright, instant cure for a frozen shoulder. I took allopathy medicines (tablets and capsules) to control the inflammation and pain. The best cure: tell your cousin to regularly go for physiotherapy sessions. I cannot emphasize enough the word 'regularly'. Unless he is committed to it, he will not get out of this problem - it would take far longer than usual if he is lax in doing physiotherapy.
Your cousin should stick to allopathy only + physiotherapy sessions + home exercises. The doctor will also prescribe an ointment which should be applied right after a warm bath in the morning and can also be applied at night before sleeping. He should be prepared for many sleepless nights. As I mentioned earlier, the pain is excruciating at night. However, under no circumstances he should rest the hand in a cast - this is a wrong thing to do. He should be prepared to go through the pain and immobility for the long haul. It can take up to a year for full mobility to return and even 2 years if he is lax in doing the exercises.
When you make a commitment, you create hope. When you keep a commitment you create trust! ~ John C. Maxwell