Are the benefits of collagen care for loss of elasticity really certain?

After dieting rapidly, I lost weight, but my face also thinned out, causing my cheeks to sink in and my skin elasticity to disappear completely. I hear so often that I look tired, so I started looking for a treatment that would naturally restore volume and became interested in collagen care programs. I heard that the biggest appeal of collagen care is that, unlike fillers which artificially inject substances, it helps your skin regenerate on its own. However, I also heard that since the plumping happens gradually over time, there are no immediate changes. I am curious to know when those who have actually received collagen care felt their skin becoming firmer. Aside from being safe and having no side effects, I would appreciate any advice on other benefits.