My son is undergoing ketamine IV therapy for his depression.

IV ketamine was a short term miracle for me as it brought me back to work which I loved. I thought it would be the answer after a lifetime of failed efforts but each successive treatment worked less and less. I stopped at 6 a few years ago. I would definitely try again as I'm in a different energy state than before but with Kaiser one has to be off of marijuana, which is the only medicine that has worked for me over time. I've asked my psychiatrist that if Kaiser changes policy, I'd love to try again.
Regarding your son, I'd go with more sessions along with a playful practice of feeding kindness to himself in whatever way plays out most natural for him. This self feeding of kindness has been the best treatment for me, along with the support of marijuana.

I’ve taken ketamine infusions for the last 4 years. Don’t be discouraged because there is a cumulative effect which will come overt time. I’m 66 and have had treatment resistant depression since college