The actual article does not show any proof of clinical efficacy, only evidence. You may think this is splitting hairs but overstated science is no better then misinformation in my opinion.
"It is clinically proven to relieve pain" - A more accurate way to phrase this is "it has shown therapeutic potential to relieve pain in a clinical setting". The original authors describe it this way also. Proofs come from equations, evidence comes from experiments.

Also bears noting that the authors mention toxicity by pyrrolizidine alkaloids contained within. The authors disregard this by saying that "It is important to note that fully licensed medicinal products available today contain depleted or PA-free processed extracts."

Therefore if any users on this website are looking at this with the intent using the plant, they should be made aware of the actual TOXICITY contained in the plant. Alcohol also dulls pain while destroying the liver.

I would also note using restraint on the term 'clinical trials'. Clinical trials are a set of trials by which potential medicines are tested before they can be allowed for release. They go from phase 1-4, testing safety and efficacy with exponentially increasing costs (In 2006 the estimated cost for phase 4 trials was $1 billion). Millions of drugs pass phase one, only a handful are even sent to phase 4. It is important not to confuse passing phase 1 with passing phase 4, it is the difference between saying you have climbed to Mt Everest base camp and saying you have climbed Mt Everest.