Sweeteners such as aspartame, sucralose, acesulfame K, saccharin and stevia have been reviewed extensively by food safety authorities and judged safe within acceptable daily intakes, which most people do not exceed. For people cutting sugar, for example to manage weight or diabetes, swapping sugary drinks for diet versions can reduce calories and protect teeth.
Research on long-term effects continues, and some health bodies advise against using non-sugar sweeteners as a long-term strategy for weight control, suggesting the goal should be reducing overall sweetness and reliance on sweet drinks. Some people report digestive upset from sugar alcohols such as sorbitol and xylitol in larger amounts.
For most adults, occasional or moderate use of approved sweeteners is fine. People with the rare condition phenylketonuria must avoid aspartame. If you have specific concerns or a health condition, discuss your choices with a doctor or dietitian.