All tendon pain would increase within hours to a day or two. Achilles pain might be “knife-like” sharp or a dull ache. With increasing dosages or duration, tendon pain would progressively worsen. When I first started TH, I started out with T3 only. This is when I really found out how T3 affected my (post flox) tendons, and it was pretty dramatic. Within days, the tendon pain increased. This was for all of my tendons throughout my body. The pain progressed over time, until by about the 3rd week, all my tendons felt “loose” or “floppy” or “soggy” to the point I was afraid I would rupture. I had read of other FQ victims talking about their tendons feeling this way, but even during my acute reaction, when I was in severe pain, my tendons hadn’t felt this “loose” feeling. It’s a really bizarre feeling and experience. T3-only really highlighted the dramatic effect of T3 on my tendons. In fact, it was while on T3-only that I felt a big “pop” occur in my left biceps tendon, resulting in severe pain radiating down my arm and up to the shoulder, eventually resulting in frozen shoulder. Over time, I found my tendon pain increased any time there was a “rapid” change in T3 or iodine, in particular, in relationship to T4. Meaning, the higher the T3 and the lower the T4, the worse this symptom would get. This rapid change in T3 could occur due to ingesting T3 medication, production of T3 due to iodine ingestion, or, significantly, T3 increases due to autoimmune thyroid flaring. Iodine, which was like “mainlining T3” for me, also produced this same tendon pain. T3 and Iodine would cause tendon pain within hours. I always knew when I had gotten an unexpected dose of extra iodine somewhere, like in foods, because my tendons would tell me. Of course flares resulted in increased tendon pain also. Increases in T4 would also affect my tendons, but because of the longer half life and decreased metabolic action, there was a milder and more delayed response of several days.