So this is from an answer to a follow-up question in the thread about Sherlock Holmes and cocaine:

There are some disputes as to how much cocaine would be contained in the original Coca Cola syrup. Mind you, what was used was a coca leaf extract, not pure cocaine, so the dosage would depend on the amount in the plant itself, which could have been affected simply by time. It's usually assumed that a single glass of Coca Cola contained between 4 - 5mg of cocaine, which is not that much (people who snorted it would use around 35mg of it for one dose). Did this have any effect on the organism? Probably yes, mainly because it seems that caffeine in some ways amplifies cocaine's effects (and a single glass of Coca Cola would have about 80mg of caffeine). Furthermore, there are other compounds in coca leaves extract that aid in the flavouring. When the backlash against the use of coca started happening, many coca-laced products went "cold turkey" and left out the extract completely - but the customers did not find these as tasty. That's why Coca Cola itself later added an extract of coca leaves which was devoid of cocaine itself. I think they might still claim they do that, not sure there.

Hope that helps a little. As far as addiction goes, cocaine does not cause much of any physical dependence, but it obviously can cause strong psychological dependence. At the end of the 19th century there was plenty of products utilising extract of coca, such as Vin Mariani, which was in many ways a precursor and direct inspiration to John Pemberton when he came up with Coca Cola. All of these were extremely popular - but it is hard to say if their consumption caused many people to show symptoms of abuse of the substance.

Did people consider soft drinks to be "healthy" in the public consciousness back then?

Sodas and soda fountains appeared in pharmacies at first, because there was a perceived health benefit from effervescent water and druggists were the people who had the knowledge of how "impregnating water with air" worked. With time, the soda machine moved up front in the pharmacy and became more or less a place of social gathering. Mixed social gathering at that and in a time of strong and vocal temperance movements - it gained and retained popularity for a long time. The fountains themselves quickly became wonderfully ornate and required extra staff to operate them (of course, later to be called "soda jerks" or as one owner of a prosperous soda fountain called them "Fizzicians")

So sodas were obviously thought to be the healthy alternative to booze, but their popularity grew alongside the industry of producing patent medicines. And of course, many famous syrups and concoctions from the soda fountain started as that, basically unregulated substances which often did not contain any informaton about their contents, but were touted as a way to cure basically anything. Pemberton's Coca Cola in 1887 had this on its label:

"COCA-COLA SYRUP AND EXTRACT For Soda Water and other Carbonated Beverages. This Intellectual Beverage and Temperance Drink contains the valuable Tonic and Nerve Stimulant properties of the Coca plant and Cola (or Kola) nuts, and makes not only a delicious, exhilarating, refreshing and invigorating Beverage (dispensed from the soda water fountain or in other carbonated beverages), but a valuable Brain Tonic and a cure for all nervous affections—Sick Head-Ache, Neuralgia, Hysteria, Melancholy, etc. The peculiar flavor of COCA-COLA delights every palate."

I can't find the nicely coloured version and it's obviously from much later, but this cover of American Druggist always encapsulates to me how entangled pharmacy and sodas were:

https://cdn.shopify.com/s/files/1/0720/2785/products/5438_1024x1024.jpeg?v=1421979893

Anybody interested specifically in this can read Anne C. Funderburg's *Sundae Best: History of Soda Fountains" which is well researched and nicely written.

You could also go to r/askscience for the more medical side of it.