Recruitment was not possible due to COVID19.

Study will define the bioavailability and short term pharmacokinetics of the principal secondary metabolites of a aqueous-ethanolic extract of H. procumbens in non-enteric and enteric capsules.

The study(n = 12) will use a one-dose design to measure bioavailability and pharmacokinetic properties of an aqueous extract of H. procumbens containing 100mg harpagoside. Plasma levels of harpagoside, harpagide, verbascoside, and 8-p-coumarylharpagide will be measured for 24 hours with blood collections taken at timed intervals.

Inclusion Criteria:- adult (at least 18 years of age);

• diagnosed with knee osteoarthritis (OA) ;
• body mass index (BMI) of less than 40;
• willing to use only the study product, and Tramadol or Tylenol as a rescue pain medication over the course of their participation in the study;
• willing and able to monitor blood glucose levels if diabetic;
• willing to abstain from caffeine-containing drinks and food before coming into a study visit;
• able to read and understand English and have the cognitive capacity to give consent;
• willing to abstain from use of the following during participation in the study: prescription and over-the-counter non-steroidal anti-inflammatory medications, (e.g., aspirin, ibuprofen, Advil, Motrin, Nuprin, Naproxen, etc.); any dietary supplements (St. John's Wort, etc.); and, grapefruit and/or products containing it.

Exclusion Criteria:- cardiovascular disease, previous myocardial infarction, stent, coronary artery bypass graft (CABG), arrhythmia, high or low blood pressure;

• recurrent stomach upset, or gastric or duodenal ulcers;
• gallstones or gall bladder disease (cholelithiasis);
• liver or kidney disease;
• alcohol use of more than two drinks per day on a regular basis;
• Coumadin or anti-platelet drug use;
• at risk for respiratory depression, history of seizures, or taking drugs that reduce the seizure threshold or may increase the risk for development of serotonin syndrome;
• pregnant or breast feeding, or intention to become pregnant during the study;
• pronounced allergies, or known allergy to study product or corn starch (placebo);
• have had an injection to treat OA within the past three months;
• currently taking NSAIDs, unless they are willing to stop for a 1-week wash-out period;
• currently on a selective serotonin reuptake inhibitor (SSRI) but are poorly stabilized, or have evidence of suicidal ideation and/or suicide attempts in the past year; and,
• reported use during the 7 days prior to study drug administration of: prescription and over-the-counter medications (e.g., NSAIDs), and any dietary supplements; grapefruit and/or its products; and, St. John's Wort.