"But because the drug comes as a liquid that needs to be injected every day, it was unlikely to be popular with patients who already had alternatives, such as pills, that were easier to take. Pharmaceutical companies did not pursue it."
There are many other molecules out there that have advanced properties but have difficult delivery methods, including some nootropics (semax, selank, cerebrolysin, etc).
There is a group though that has no problem injecting things into themselves: bodybuilders and athletes. Fortunately for us, they have brought some other abandoned molecules back from the dead, mostly ones that heal injuries.
For example, there is a molecule found in human gastric juices, known as Body Protecting Compound 157 (BPC-157). Part of the intestinal lining has to regenerate itself nearly weekly. This compound, isolated from there, and then synthesized, is used prolifically by athletes/bodybuilders with tendon/ligament injuries, but can also be used for repairing stomach issues. etc. It is widely available on the internet. Here is the science for you:
"As has been demonstrated for many organoprotective agents using different models of various tissue lesions, despite the poorly understood final mechanism, practically all organ systems appear to benefit from BPC activity. These effects have been achieved in many species using very low dosages (mostly microgram and ng/kg range) after ip, ig, and intramucosal (local) application. The effect was apparent already after one application. Long lasting activity was also demonstrated. BPC was highly effective when applied simultaneously with noxious agents or in already pathological, as well as chronical, conditions. Therefore, it seems that BPC treatment does not share any of the so far known limitations for 'conventional organoprotectors'. No influence on different basal parameters and no toxicity were observed. These findings provide a breakthrough in stress theory. BPC, as a possible endogenous free radical scavenger and organoprotection mediator, could be a useful prototype of a new class of drugs, organoprotective agents." https://www.ncbi.nlm.nih.gov/pubmed/8298609
"Pentadecapeptide BPC 157, composed of 15 amino acids, is a partial sequence of body protection compound (BPC) that is discovered in and isolated from human gastric juice. Experimentally it has been demonstrated to accelerate the healing of many different wounds, including transected rat Achilles tendon. This study was designed to investigate the potential mechanism of BPC 157 to enhance healing of injured tendon." https://www.physiology.org/doi/full/10.1152/japplphysiol.009...
"BPC 157 may serve as a novel mediator of Robert’s cytoprotection, involved in maintaining of GI mucosa integrity, with no toxic effect. BPC 157 was successful in the therapy of GI tract, periodontitis, liver and pancreas lesions, and in the healing of various tissues and wounds." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5333585/
" A novel stomach pentadecapeptide, BPC-157, improves wound and fracture healing in rats in addition to having an angiogenic effect. Therefore, in the present study, using a segmental osteoperiosteal bone defect (0.8 cm, in the middle of the left radius) that remained incompletely healed in all control rabbits for 6 weeks (assessed in 2 week intervals), pentadecapeptide BPC-157 was further studied (either percutaneously given locally [10 microg/kg body weight] into the bone defect, or applied intramuscularly [intermittently, at postoperative days 7, 9, 14, and 16 at 10 microg/kg body weight] or continuously [once per day, postoperative days 7-21 at 10 microg or 10 ng/kg body weight])...Pentadecapeptide BPC-157 significantly improved the healing of segmental bone defects." https://www.ncbi.nlm.nih.gov/pubmed/10071911
"BPC 157 improved muscle healing, macroscopically (less hematoma and edema, no post-injury leg contracture), microscopically, functionally, and also based on enzyme activity (creatine kinase, lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase)...BPC 157, at all investigated intervals, given locally or intraperitoneally, accelerated post-injury muscle healing and also helped to restore the full function." https://www.ncbi.nlm.nih.gov/pubmed/18668315