I'm not arguing with someone's personal experience, but I found the following on Wikipedia:
Some alternative medicine proponents claim that serratiopeptidase is beneficial for pain and inflammation[3] but there is no compelling evidence.[4] Online medical journal Bandolier (specializing in Evidence-based thinking about healthcare)[5] published an article (in about 2001) in response to a reader's enquiry about serratiopeptidase.[6] After searching PubMed and the Cochrane Library "to see if there are any randomised, controlled trials", the article stated that the "evidence on serratiopeptidase being effective for anything is not based on a firm foundation of clinical trials."[4]
The search found 34 publications in the medical databases covered, that addressed the efficacy of serratiopeptidase, of which several were found to be animal experiments, personal letters, uncontrolled trials or those with inadequate or nonexistent randomisation. The article warned against ignoring safety issues with use of biological agents.[4] No studies were found to have been conducted on the efficacy of serratiopeptidase as treatment for back pain, heart attack, stroke, or asthma. Of the 10 medical conditions with randomized-evidence studies on file in connection with serratiopeptidase, trial quality was described as "generally poor".[4][7]
#7 According to Bandolier:
"Studies were small, outcomes were poorly defined, and in some, different medical conditions were mixed. Five studies were described as double blind: one was completely uninterpretable, three methodologically weak studies were positive, and one trial of apparent high quality was negative. This latter study compared serratiopeptidase, serraprose S or placebo in the treatment of chronic respiratory disease, with about 120 patients per group, and found no significant difference between groups for any outcome."
- Bandolier, "Serratiopeptidase - Finding the Evidence"