Theres something that your mate is not telling you .
Doctors have a patient confidentiality for them to contact the police on such matters there has been something said, with regard to your mates condition , it could also be someone in his family that has approached the GP with reference to his well being.
IE along the line of the pain is to much that he could get the gun out the cupboard and shoot myself is all it would take .
This could have been said out of context who knows, it could be something totally different . its no good you surmising what was said ,he should go to the GP and find out what the script is, taking a witness to the fact with him ,if the drugs he is taking are of such a nature that he cannot work machinery or he cannot drive there are in some cases ,where the GP is driven by a care and duty to others, must contact the appropriate authorities for the removal of driving licenses and certificates for a period of time agreed by him and his patient, unless there is a mental health issue .
Ive been there having had Cancer twice ,the second time was extremely close to the box I put all the weapons in to my fathers cabinets in case the light had gone out, then my wife wouldn't have had any further problems , i contacted the police at that time they didn't see the need for that to happen but could see the reason behind it.