I've been on and off minocycline for nearly a year and a half, and I took it continuously for 6 months at a time, including 3 months at 400mg/daily. I take it because it suppresses my joint (mainly left knee) pain and decreases my brain fog to tolerable levels and cuts my tendency towards depression and fatigue. At 400 mg/daily I could literally feel my IQ expanding every week, and my short and long term memory improved as well, and at that level it was equivalent to 2000mg of IV cephtriaxone/daily in its perceived effect, but I usually take it at 200mg/daily or 300mg/5 days week. Although I was infected with Lyme Disease, I have/had many MS like symptoms and the intense joint pain did not begin until 14 years after the initial infection.
If you take it, make sure you also take an effective form of acidophilus, eat lots of plain yogurt, and lots of green leafy vegetables and salads - cut out the sweets or GI tract problems can occur when on a steady regimen of minocycline. Despite what the Dr might say, it is OK to take with milk, and in fact I cannot tolerate it without food, so I take it mid meal. Try and be active for a hour or so after taking it, and avoid lying down during that hour. The only real side effect I've noticed is that it tends to give me a very dark tan, and causes some minor pigmentation spots on my arms. you should avoid prolonged sun exposure.