24, is it possible to completely reverse facial volume loss in cheeks? (Photos)

Yes, you can regain the fullness, but it has to be done with fat grafting and injectables. Fat grafting needs to be repeated in 3 years - 5 years, and injectables once a year. There is no medicine or drug that you can take to reverse what you have. I assume that you had a medical work up to rule out any medical reason for fat loss. While I do not advocate for smoking, I doubt that it was the cause of your fat loss You have hope as what you have can be corrected in minutes

There are different ways of augmenting cheeks; volume can be increased by means of fillers or fat micro and na o grafts. It would be in your best interest to seek a consultation ( in-person or teleconference) with a board certified plastic surgeon with extensive experience in facial and periorbital fat grafting. Good luck.

Thank you Monica for posting your question here,I will start by stating that my answer is based on the limited information and pictures provided , for a more bespoke plan please consult with your plastic surgeon in person.
Your assessment is correct, smoking and weight loss can age the face , and lead to volume loss in the cheeks , but you should not despair there are many ways to restore volume from fillers and bio-stimulators to fat transfer.
I personally prefer fat transfer , it gives the most natural results and does not cause much inflammation like bio-stimulators or potentially migrate like fillers. That being said I would recommend consulting with your surgeon to assess if you are a good candidate for fat transfer.I hope this helps! Best of luck!