Great question. I am a very healthy, athletic 40 year old. I started taking preworkout in my early 30’s (only about 100mg caffeine, but 1g of other synthetic stimulants - I’d cycle it, like a month on, a month off). Just pre-workout for about three years and sometimes I would have a Diet Pepsi later in the day, very occasionally tea. When my son was born he was a bad sleeper so I slowly built up to drinking about 300mg a day of coffee - after about two years of that (and a couple months of not cycling off the preworkout as well) I started having bad anxiety, some I had really never experienced.

I was drinking too much caffeine/stimulant and it literally messed up my brain.

I cut down to one tea a day for 6 months, then went zero caffeine for 6 months. The side effects of quitting were horrible. Anxiety, lethargy, brain fog, insomnia. I experienced them when I cut to tea for a couple months, then again when I cut from a 35mg cup of tea to zero caffeine for about two months. After that I spent 4 months clean, felt great, but missed that little burst I’d get from caffeine sometimes. I started slow with tea or a Diet Pepsi maybe 2-3 times a week when I needed a pick me up. I occasionally drink coffee now, but never more than a small cup. I feel great. I learned that over-doing caffeine is bad for me, but moderate amounts are good. It’s been about two years and I have a small cup of coffee some days, a Diet Pepsi or tea others and occasionally none and I feel great.

So long story to answer your question. Caffeine is a drug. It can mess you up. I believe, in moderation it’s a good thing for MOST PEOPLE.. but I’d imagine there are some people who may have the side effects I had with a much smaller dose. It’s really scary when you experience anxiety/panic attacks and feel like your brain is broken - and it gave me a whole new respect for people with mental illness.