In practice, “longevity shot” can mean several very different things: a vitamin injection, a pain-control injection, subcutaneous fluids, or a clinic-administered supplement. None of these are proven to extend lifespan in healthy cats as a general rule. The more evidence-based framing is cat longevity support: lowering avoidable stressors on the body while keeping daily function cleaner, more rhythmic, and easier to assess.
At home, it helps to translate marketing into concrete questions: What problem is being targeted—pain, appetite, hydration, anxiety, or a diagnosed disease? How will the household know it worked—jump height, grooming time, litter box output, or weight trend points? Natural longevity alternatives cats can use daily often fit better than episodic injections because they create a routine that can be monitored and adjusted.