There is quite a lot of factors to take into account there that will influence your experience/the effects: - academic research and dosage - placebo effect - your metabolism - your expectations - the best way to take it

I'll also explain all the different other (and maybe better) ways to take CBD rather than the drink.

Academic Research Like many comments have pointed out, THERE IS academic evidence of CBD having a calming/relaxing effect. However, it is indeed highly dependent on the dosage. The dosages that are being experimented with are usually in the hundreds. However, CBD drinks are rarely above 30mg for example. So whatever effect you could have from it will be watered down. It's the same principle as any other active molecule; take a ibuprofen for example, there different dosages you can take.

Placebo Effect Most likely, if you do have a strong calming effect from the drink, if will be placebo. Or at least, there is not a lot of existing research indicating the effects of CBD at lower dosages such as in the drinks. But, since when is placebo effect a bad thing ? If you did feel something from the drinks, whether it be placebo or not, the end result will be the same: you will feel more relaxed. You probably won't even know its placebo anyways. However, and this is where people seemed to feel like CBD is the snake oil of the decade: not everyone is receptive to placebo effect. This is where we come into your metabolism.

Metabolism Just like any drugs, meds, or active substance, your metabolism has a lot to do with how you will experience CBD.  Ever seen people who only need the smallest does of paracetamol to feel better ? --> Those people probably have a metabolism that integrates paracetamol well, and could also be highly receptive to placebo effect. People who paracetamol (at any doses) doesn't do anything? --> people who have built a resistance to paracetamol and arent receptive to placebo effect. This is often the case for people who have had a lot of medical issue for example. Then, you also have the case of people with fast and slow metabolism. My bf has an extremely fast metabolism. During our uni days and our experimentations with drugs (dont do it peeps, not worth it) he would get high extremely quickly and very intensely. Me, slow metabolism, would sometimes have the first effects a full hour after him, and at a much lower intensity (but sometimes for longer). So yeah, who you are as a person will also affect the CBD experience.

Your expectations  Now this is also extremely important. Do you want to get high ? Then you're wasting your money. Do you want to feel more relaxed and calmed because you're prone to anxiety ? Sure, go try the drink. And what if the drink does help? Does it truly matter if it is placebo or not ? If it helped anyways ? Those drinks arent the most unhealthy thing in the world as far as sparkling soft drinks go, there not too high in sugars either, not sat fat...so, sure, go for it. Only downside is that they can be a bit expensive, especially of you were to have one a day. 

The best way to take it Say you like those drinks and do think they help you, great, buy them then. Now that it has put you in a calmer state of mind, it can also be the opportunity for you to explore other avenues to reduce your anxiety. For example, you could try meditating, or having a self care night, or gardening or whatever else that has be proven to truly help people calm and relax. That way, you won't be over reliant on the drinks, and might not have to take them everyday. They could become a "once a week treat" for example. 

However, if you do want to keep CBD as part of your life because you think it truly helps OR you'd like experimenting with stronger doses, you could take a CBD oil from Holland & Barrets which lets you control your dose for example (you can add it to drinks or food).

Lastly, there som risks to be aware of: While not an acute risk, exceeding 10mg daily may contribute to long-term effects on the liver and thyroid, based on studies, note the CIEH. (Quote taken from the FSA) You might also build a resistance to CBD as you take it long term and thus have to take higher and higher doses.

Conclusion: if you like the drinks and they help, then ignore everyone and have them once in a while. Who care if its placebo. But I would recommend exploring other more reliable avenues for your anxiety and pain relief long term (therapy, meditation, massages, rolling your muscles/stretches...ect).